The link between the two epidemics provides an opportunity to remedy obesity while dealing with Covid-19.

The World Health Organization proclaimed the global epidemic of obesity more than twenty years ago. However, there has never been a coordinated action to address the problem on the global level. Covid-19 virus pandemic is world's largest public health problem currently. Many comorbidities associated with Covid-19 and obesity mortality are common. We determine that obesity is single largest and most common cause of mortality in Covid-19 patients globally based on a sample of 171 countries, while economic variables have no impact. This creates an opportunity to finally address the obesity global epidemic through an effort coordinated on the global level.

Introduction

Obesity is a complex disease involving an excessive amount of body fat (Mayo Clinic, 2022). The World Health Organization (WHO) described obesity as a global epidemic more than twenty years ago (World Health Organization, 2000a). The problem remains as continuous global increase of obesity did not subside. In 2016, more than 1.9 billion or 39% of adults aged 18 years and over (39% of men and 40% of women) were overweight (World Health Organization, 2020b). Of these, over 650 million adults were obese. That translates into about 13% of the world’s adult population (11% of men and 15% of women) were obese in 2016. In addition, over 340 million children and adolescents aged 5–19 and an estimated 38.2 million children under the age of 5 years were overweight or obese in 2016 (World Health Organization, 2020b). Global epidemic implies that the problem exists on all continents and in almost all countries, with a few exceptions in Sub-Saharan Africa and Asia (World Health Organization, 2020b). It has been long hypothesized and confirmed that globalization is a major contributor to spreading of obesity and diet-related chronic diseases globally (e.g., Miljkovic, Shaik, Miranda, Barabanov, & Liogier, 2015; Miljkovic, de Miranda, Kassouf, & Oliveira, 2018; Oberlander, Disdier, & Etilé, 2017). If we understand globalization as a process by which national/regional economies, societies and cultures have become integrated through a global network of economic, technological, socio-cultural, political and biological factors (Croucher, 2018), rather than the trade liberalization only, the possibility of its resulting externalities, including increasing rate of obesity, rises significantly (Miljkovic et al., 2015).

Overweight and obesity are major causes of many comorbidities which can lead to further morbidity and mortality. For example, increased overweight and obesity have been associated with increased death rates for all cancers combined and for cancers at multiple specific sites (Calle, Rodriguez, Walker-Thurmond, & Thun, 2003). Furthermore, increasing body mass index (BMI), as a standard measure of obesity in adults, is associated with glucose intolerance, dyslipidemia, hypertension, type 2 diabetes, kidney failure, and osteoarthritis (Martin-Rodriguez, Guillen-Grima, Martí, & Antonio, 2015). Moreover, all degrees of obesity are associated with asthma, heart failure, and severe mental disorders. Type II and morbid obesity are associated with chronic obstructive pulmonary disease and depression (Martin-Rodriguez et al., 2015).

The WHO has declared the novel coronavirus SARS-COVID-19–2 (COVID-19) outbreak a global pandemic on March 11, 2020 (Cucinotta & Vanelli, 2020). The virus has wreaked havoc worldwide, bringing the life we know to almost a halt. Studies to date show that advanced age and the presence of one or more underlying health conditions are risk factors for increased severity of the disease (Hussain, Mahawar, Xia, Yang, & Shamsi, 2020). Many of the underlying conditions considered as the risk factors for increased mortality due to COVID-19 are ones and the same as the comorbidities associated with increased obesity and overweight (Hussain et al., 2020; Martin-Rodriguez et al., 2015).

We empirically test and demonstrate in this paper that higher obesity rates indeed cause an increase in mortality rates in those infected by COVID-19 globally. Moreover, we also demonstrate that, on global level, high obesity rates are the primary cause of higher mortality rates due to COVID-19. This also holds true across all COVID-19 mortality rate quantiles and after controlling for several other comorbidities or exogenous factors. As obesity is a non-contagious disease, it has always been difficult to establish international standards on how to address the problem. Considering findings on causal linkage between obesity and COVID-19 mortality, we propose more wholistic policies to combat global obesity with the goal to decrease comorbidities and mortality rates associated with both obesity and COVID-19.

Data and methodology

Data and variables description

There are 171 countries in the sample, and they are listed in the Appendix. The definition of and sources for each variable are provided in Table 1.

Table 1

Variables description and source.

Variable	Description	Source
death	COVID-19 attributed deaths (per-million) cumulated until 08/01/2021	European CDC
obesity	Percentage of adult obesity in the country (in 2016) (most recent observation)	WHO, Global Health Observatory
hdi	Country’s Human Development index (most recent observation for each country within the last five years)	World Bank
over65	Population ages 65 and above (% of total population) (in 2019)	World Bank
vaccination	Percentage of population with at least 1 dose (until 08/02/2021)	NCD Risk Factor Collaboration
pop_density	Population density (people per sq. km of land area) (in 2019)	World Bank

Causality between the obesity rates and mortality rates due to COVID-19

We use the methods of Directed Acyclic Graphs (DAGs) (Imbens, 2020; Judea., 1995, Pearl, 2000; Pearl and Mackenzie, 2018) to test for causality between the COVID-19 attributed deaths (per-million) and variables representing major comorbidities including the adult obesity and the share of the at-risk population based on the advanced age (Hussain et al., 2020). Control variables used are each country’s human development index (HDI), COVID-19 vaccination rate, and population density in the country.

DAGs represent, “…principled, nonparametric framework for causal inference, in which diagrams are queried to determine if the assumptions available are sufficient for identifying causal effects from non-experimental data. If so, the diagrams can be queried to produce mathematical expressions for causal effects in terms of observed distributions; otherwise, the diagrams can be queried to suggest additional observations or auxiliary experiments from which the desired outcomes can be obtained” (Pearl, 1995, p. 669). These causal relations are determined by computer algorithms which produce graphs with nodes (vertices, variables) and edges between nodes. Visually, a DAG is a graph, which is an ordered triple 〈V, M, E〉. Here, V is the vertex set, which is a non-empty set that contains nodes, M is a non-empty set of marks which shows the directedness of an edge, and E is the edge set, containing ordered pairs representing edges between nodes (Ramsey, Glymour, Sanchez-Romero, & Glymour, 2017). These edges indicate a causal relationship between nodes and can be either directed or undirected edges (indicated by the marks). For two arbitrary nodes A and B, with a directed edge (indicated by a line with an arrow) from node A to node B, we can say that node A is a cause of node B. For an undirected edge (indicated by a line between nodes) between node A and node B, we can say one of the following: a) node A is a cause of node B, b) node B is a cause of node A, c) there is some unmeasured confounder of A and B, d) both a and b, or e) both b and c.

For the DAG method, the search for the edges depends on the algorithm and one might find different outcomes based on the algorithm used. In this study we use LiNGAM (Shimizu, Hoyer, Hyvärinen, & Kerminen, 2006) which is one of the first of the algorithms that assumed linearity among the variables and non-Gaussianity of error term and is one of the most used for smaller models as is the case of the present study. The underlying idea for this searching method is to use the Independent Components Analysis (ICA) algorithm to check all permutations of the variables to find one that is a causal order, that is, one in which earlier variables can cause later variables but not vice-versa. For the implementation of ICA we use is FastIca (Hyvärinen, Karhunen, & Oja, 2004). Since we assume the model is a DAG, there must be some permutation of the variables for which the main diagonal of the inverse of the weight matrix contains no zeros. In addition, a lower triangular weight matrix provides evidence of a causal order. Once a causal order is being established, the next step is to eliminate the extra edges. For this, we use the causal order to define knowledge of tiers and run Fast Greedy Equivalence Search (FGES). The implementation of LiNGAM has one parameter, penalty discount, used for the FGES adjacency search. The method as implemented does not scale much beyond 10 variables, making it very suitable for models with a small number of variables as is the case of the present study. We check the robustness of DAGs’ using the FASK algorithm (Sanchez-Romero et al., 2018) finding similar results. These results are generally consistent with the LiNGAM algorithm outcomes and available from the authors upon the request. We also test the results in different contexts, meaning with and without imposing prior knowledge regarding the causal relationship between percentage of people vaccinated and COVID-19 attributable mortality.

We used TETRAD software version 6.9.0 in our DAGs analysis. Five optimizers can be used to search the configurations of parameters: Powell, EM, RICF, accurate regression, and random search. We used “accurate regression” estimates which presuppose that the input parametric model is a DAG, and its associated statistics are based on a linear, non-Gaussian model. The results did not change when using other optimizer algorithms.

Quantile regression

DAGs analysis results, in addition to their significance on their own, are used as the identification strategy to test the hypothesis of obesity on mortality from the COVID-19 in resulting regression analysis. Quantile regression (Koenker and Bassett, 1978, Koenker and Hallock., 2001) is used to determine if the positive impact of adult obesity persists across the quantiles of the COVID-19 attributed mortality rates. The quantile regression is a method that provides parameter coefficients estimation for any quantile in the range of zero and one (0,1) conditional on the exogenous variables. Where a simple ordinary least square regression is based on the mean of the distribution of the regression’s variable, the quantile regression assumes that the possible difference in terms of the impact of the exogenous variables along the conditional distribution is important.

Results

Two different models are analyzed for the period starting at the beginning of the pandemic through February 01, 2022: first assumes that vaccinated people are those who received at most two shots of the vaccine, while the second includes those who received booster dose as well. First, we focus on results of the model where vaccination implies at most two doses of a vaccine received. The DAGs indicate that there is unidirectional causality going from both adult obesity and larger older population share towards the COVID-19 attributed mortality rate. Associated statistics indicate that both of these variables are most and equally important causes of the COVID-19 mortality rate worldwide. The level of socio-economic development as measured by the HDI has no direct causal link with the COVID-19 attributed mortality rate. The DAG produced that result while imposing prior knowledge. HDI, however, does cause an increase in obesity rates in adults but also the longer life, as measured by an increase in the share of population over the age of 65. Hence, one might say how there is an indirect causality of relative affluence on increase in COVID-19 attributed mortality rate. This finding has important implications on targets of global policies directed at alleviating global both obesity and COVID-19 epidemics. Finally, there is no causality from vaccination rates to COVID-19 attributed mortality rates, while the relative level of affluence as measured by the HDI leads to higher vaccination rates. Population density has no causal relationship with any of the considered variables including COVID-19 attributed mortality rates.

Although we considered other variables in the preliminaries of this study (e.g., number of hospital beds, macro-economic variables), their inclusion in the final analysis would be to the detriment of the number of countries that could be examined in the study. In other words, due to the lack of data, there is a trade-off between a more comprehensive approach to the causality of the COVID-19 attributable diseases and a broader examination that could bring most countries into the analysis (which is the scope of the present study). In addition to that, variables such as GDP or number of hospital beds are also indicators of the level of economic development and are highly correlated with but less comprehensive than the HDI. Hence, most comprehensive economic development indicator/variable (HDI) is selected in the model.

Figure 1 contains the DAG while the associated statistical results are provided in Table 2.

Fig. 1

Causality using DAGs through February 01, 2022.

Table 2

Statistical results associated with DAG in Fig. 1.

From	To	Type	Value	SE	Ta	Pa
older65	obesity	Edge Coef.	-0.42	0.17	-2.48	0.015
older65	deaths	Edge Coef.	68.76	17.43	3.95	0.000
hdi	older65	Edge Coef.	36.36	3.33	10.94	0.000
hdi	obesity	Edge Coef.	50.04	8.20	6.10	0.000
hdi	vaccinated	Edge Coef.	144.45	11.08	13.04	0.000
obesity	deaths	Edge Coef.	44.86	13.40	3.35	0.001

Null hypothesis for T and P is that the parameter is zero.

We now turn to the second model which includes those who received not only two vaccine shots but a booster dose as well. These results remain similar but with one fundamental difference: larger share of the population older than 65 does not cause increase mortality from COVID-19. This has important implications as older population seems to be better protected due to booster shot from COVID-19 and thus less vulnerable. Obesity, however, remains the key direct causal contributor to mortality from COVID-19. The level of economic development as presented by HDI has two important indirect causal impacts on mortality from COVID-19, moving in opposite directions. Just like before, relative affluence leads to increased obesity levels and, in turn, increased mortality from COVID-19. However, higher HDI also implies larger share of older population and causes more booster vaccines being inoculated. In this case, it seems that the larger affluence level does serve as a protector of older population via high rates of booster shots injected. Fig. 2 contains the DAG while the statistical results are provided in Table 3 associated with this model.

Fig. 2

Causality (including booster) using Directed Acyclic Graphs through february 01, 2022.

Table 3

Statistical results associated with DAG in Fig. 2.

From	To	Type	Value	SE	Ta	Pa
hdi	older65	Edge Coef.	51.82	5.41	9.57	0.000
hdi	obesity	Edge Coef.	24.46	3.32	5.88	0.000
hdi	boosters	Edge Coef.	144.65	18.31	7.90	0.000
obesity	deaths	Edge Coef.	50.77	19.94	2.55	0.013

Null hypothesis for T and P is that the parameter is zero.

Results from the DAGs analysis are used in this step to facilitate proper econometric model specification and serve as an indirect test for endogeneity (Miljkovic, Dalbec, & Zhang, 2016). Quantiles have been designated in 10 percentile increments. The results are reported in Table 4.

Table 4

Results of the quantile regression accounting for fully vaccinated (including booster) – period through 02/01/2022.

	Deaths	Coef.	Std. Err.	T	P > t	[95% Conf. Interval]
q10
	obesity	37.69894	25.71025	1.47	0.148	-13.71188	89.10975
	hdi	-4095.171	4890.102	-0.84	0.406	-13873.53	5683.192
	older_65	58.3222	62.37209	0.94	0.353	-66.3985	183.0429
	density	0.0821239	0.2114574	0.39	0.699	-0.3407112	0.5049591
	boosters	4.034748	12.32981	0.33	0.745	-20.62023	28.68973
	_cons	2130.156	2728.813	0.78	0.438	-3326.444	7586.756
q20
	obesity	44.26472	28.5701	1.55	0.126	-12.86473	101.3942
	hdi	-4241.41	4152.61	-1.02	0.311	-12545.07	4062.247
	older_65	48.74619	46.4024	1.05	0.298	-44.04115	141.5335
	density	0.0577842	0.2755103	0.21	0.835	-0.4931327	0.6087012
	boosters	4.766522	13.01408	0.37	0.715	-21.25674	30.78978
	_cons	2501.206	2502.67	1	0.322	-2503.193	7505.604
q30
	obesity	48.85427	31.63664	1.54	0.128	-14.4071	112.1156
	hdi	-5363.919	4591.916	-1.17	0.247	-14546.02	3818.185
	older_65	103.4288	36.30801	2.85	0.006	30.82645	176.0312
	density	0.0180793	0.3221949	0.06	0.955	-0.6261891	0.6623477
	boosters	8.845031	17.28128	0.51	0.611	-25.71102	43.40109
	_cons	2897.05	2885.193	1	0.319	-2872.249	8666.35
q40
	obesity	58.0678	32.32598	1.8	0.077	-6.571984	122.7076
	hdi	-3106.805	4579.69	-0.68	0.5	-12264.46	6050.851
	older_65	106.5823	33.48615	3.18	0.002	39.62258	173.542
	density	0.0202932	0.3088481	0.07	0.948	-0.5972868	0.6378732
	boosters	-6.589368	17.57216	-0.37	0.709	-41.72707	28.54833
	_cons	1561.368	3102.309	0.5	0.617	-4642.082	7764.818
q50
	obesity	59.84839	24.53064	2.44	0.018	10.79636	108.9004
	hdi	-2696.429	3972.403	-0.68	0.5	-10639.74	5246.882
	older_65	107.7603	29.99376	3.59	0.001	47.78404	167.7365
	density	0.0245441	0.3984906	0.06	0.951	-0.7722872	0.8213754
	boosters	-15.09388	14.43882	-1.05	0.3	-43.96608	13.77832
	_cons	1610.39	2595.167	0.62	0.537	-3578.969	6799.748
q60
	obesity	66.26767	20.03735	3.31	0.002	26.20052	106.3348
	hdi	-2580.356	2861.683	-0.9	0.371	-8302.645	3141.932
	older_65	102.0046	31.58909	3.23	0.002	38.83829	165.1709
	density	0.0216915	0.4109722	0.05	0.958	-0.8000982	0.8434811
	boosters	-14.31505	14.89014	-0.96	0.34	-44.08973	15.45964
	_cons	1514.1	1928.888	0.78	0.436	-2342.95	5371.15
q70
	obesity	68.68129	24.94501	2.75	0.008	18.80066	118.5619
	hdi	-2348.03	3455.81	-0.68	0.499	-9258.351	4562.29
	older_65	117.7891	49.29748	2.39	0.02	19.21273	216.3655
	density	0.0022799	0.4861505	0	0.996	-0.9698381	0.9743979
	boosters	-17.36967	15.29658	-1.14	0.261	-47.95707	13.21772
	_cons	1408.465	2222.892	0.63	0.529	-3036.483	5853.413
q80
	obesity	93.80904	28.50039	3.29	0.002	36.81899	150.7991
	hdi	-6985.961	6448.096	-1.08	0.283	-19879.73	5907.805
	older_65	181.1685	51.22136	3.54	0.001	78.74509	283.592
	density	0.0394962	0.7738799	0.05	0.959	-1.507972	1.586965
	boosters	-13.22364	22.0369	-0.6	0.551	-57.28914	30.84185
	_cons	4251.304	4388.66	0.97	0.337	-4524.364	13,026.97
q90
	obesity	87.44192	44.74705	1.95	0.055	-2.035339	176.9192
	hdi	-12334.61	7165.033	-1.72	0.09	-26661.98	1992.76
	older_65	210.1969	61.08509	3.44	0.001	88.04972	332.3441
	density	0.0516366	0.7567624	0.07	0.946	-1.461603	1.564877
	boosters	-9.649906	21.58764	-0.45	0.656	-52.81707	33.51725
	_cons	8628.516	4604.415	1.87	0.066	-578.5801	17,835.61

The results indicate that strong positive relationship between the adult obesity rates and the COVID-19 attributed deaths persists at 10% significance level or lower for all but the lowest thirty percentile. Coincidentally, countries with lowest mortality rates are also the countries with lowest prevalence of obesity. An important policy implication of this result is its global nature thus enabling universal policy that could address both obesity and COVID-19 epidemics globally.

The results indicate that strong positive relationship between the adult obesity rates and the COVID-19 attributed deaths persists at 10% significance level or lower for all but the lowest thirty percentile. An important policy implication of this result is its global nature thus enabling universal policy that could address both obesity and COVID-19 epidemics globally.

The relationship between the share of 65 and older population and the COVID-19 attributed mortality rates is equally transparent. It is positive and statistically significant at 5% or lower significance level at all but the lowest 20 percentiles only. This result is consistent with the DAGs established in the first model, positive causation between the share of 65 and older population and the COVID-19 mortality rates. Finally, no significant correlations at any percentile but the 90th are observed between the HDI and mortality rates, and none at all between the vaccination rate or population density and the COVID-19 attributed mortality rates.

Robustness check

The robustness of the results is checked by running the analysis for the period from the beginning of the pandemic through August 01, 2021, i.e., the early vaccination stage. We consider people who received at least one dose of a COVID-19 vaccine. The results are qualitatively identical to those of the double vaccinated population on February 01, 2022.

The DAGs and associated statistics are presented in Figure 3 and Table 5, respectively.

Fig. 3

Causality (at least once-vaccinated) using DAGs through august 01, 2022.

Table 5

Statistical results associated with DAG in Fig. 3.

From	To	Type	Value	SE	Ta	Pa
older65	adult obesity	Edge Coef.	-0.51	0.19	-2.68	0.009
older65	deaths	Edge Coef.	40.34	14.79	2.98	0.004
hdi	older65	Edge Coef.	43.09	3.61	11.76	0.000
hdi	adult obesity	Edge Coef.	60.09	10.32	5.88	0.000
hdi	vaccinated	Edge Coef.	137.19	14.87	9.40	0.000
adult obesity	deaths	Edge Coef.	34.18	10.99	3.03	0.003

Null hypothesis for T and P is that the parameter is zero.

Results from the DAGs analysis are again used in this step to facilitate proper econometric model specification and serve as an indirect test for endogeneity (Miljkovic et al., 2016). The results from the quantile regression are reported in Table 6.

Table 6

Results of the quantile regression-period through 08/01/2021.

Quantile/variable	Coefficient	Std. Err.	t	P-value	[95% confidence interval]
q10
adult obesity	8.64	12.0	0.72	0.47	-15.2	32.5
older_65	9.87	18.3	0.54	0.59	-26.5	46.2
vaccination	1.62	4.9	0.33	0.74	-8.2	11.5
hdi	-367.92	881.0	-0.42	0.68	-2120.6	1384.7
pop_density	0.00	0.1	-0.04	0.97	-0.2	0.2
cons	89.77	388.4	0.23	0.82	-682.8	862.4
q20
adult obesity	17.31	14.7	1.18	0.24	-11.8	46.5
older_65	44.83*	23.8	1.88	0.06	-2.5	92.2
vaccination	3.11	5.3	0.59	0.56	-7.5	13.7
hdi	-1390.02	959.2	-1.45	0.15	-3298.2	518.2
pop_density	-0.01	0.1	-0.11	0.91	-0.2	0.2
cons	503.43	541.4	0.93	0.36	-573.6	1580.5
q30
adult obesity	24.49*	13.3	1.97	0.05	-2.0	51.0
older_65	69.22***	24.2	2.87	0.01	21.2	117.3
vaccination	-0.43	6.1	-0.07	0.94	-12.6	11.8
hdi	-1214.82	1085.7	-1.12	0.27	-3374.6	944.9
pop_density	-0.02	0.1	-0.26	0.80	-0.2	0.2
cons	327.43	513.9	0.64	0.53	-695.0	1349.8
q40
adult obesity	31.83***	11.8	2.70	0.01	8.4	55.3
older_65	69.81***	24.3	2.87	0.01	21.4	118.2
vaccination	-2.13	5.5	-0.39	0.70	-13.1	8.8
hdi	-1205.47	1512.1	-0.80	0.43	-4213.5	1802.6
pop_density	-0.02	0.2	-0.16	0.88	-0.3	0.3
cons	389.23	785.4	0.50	0.62	-1173.3	1951.7
q50
adult obesity	34.09***	12.5	2.73	0.01	9.2	59.0
older_65	87.64***	26.1	3.36	0.00	35.8	139.5
vaccination	-1.12	5.7	-0.20	0.84	-12.4	10.2
hdi	-1717.06	1402.8	-1.22	0.22	-4507.6	1073.5
pop_density	-0.03	0.1	-0.24	0.81	-0.3	0.2
cons	630.98	716.4	0.88	0.38	-794.2	2056.2
q60
adult obesity	49.31***	12.2	4.04	0.00	25.0	73.6
older_65	104.75***	28.5	3.67	0.00	48.0	161.5
vaccination	-0.72	6.8	-0.11	0.92	-14.3	12.9
hdi	-2932.13*	1764.7	-1.66	0.10	-6442.6	578.3
pop_density	-0.01	0.2	-0.04	0.97	-0.4	0.4
cons	1222.35	888.2	1.38	0.17	-544.6	2989.3
q70
adult obesity	46.92***	14.0	3.35	0.00	19.1	74.8
older_65	71.57*	38.0	1.89	0.06	-3.9	147.1
vaccination	-2.71	6.7	-0.40	0.69	-16.1	10.7
hdi	-654.43	2565.7	-0.26	0.80	-5758.5	4449.6
pop_density	-0.06	0.2	-0.28	0.78	-0.5	0.4
cons	97.74	1386.5	0.07	0.94	-2660.4	2855.9
q80
adult obesity	65.11***	23.7	2.75	0.01	18.0	112.3
older_65	65.98*	37.5	1.76	0.08	-8.7	140.6
vaccination	-4.17	6.1	-0.68	0.50	-16.3	8.0
hdi	-609.90	3090.6	-0.20	0.84	-6758.0	5538.2
pop_density	-0.06	0.2	-0.32	0.75	-0.4	0.3
cons	125.34	1638.1	0.08	0.94	-3133.3	3384.0
q90
adult obesity	71.74**	36.3	1.98	0.05	-0.4	143.9
older_65	49.53	108.4	0.46	0.65	-166.1	265.2
vaccination	-1.26	14.4	-0.09	0.93	-29.9	27.4
hdi	124.78	6926.0	0.02	0.99	-13,653.3	13,902.9
pop_density	-0.10	0.5	-0.22	0.83	-1.0	0.8
cons	-279.24	3011.4	-0.09	0.93	-6269.8	5711.4

Number of observations: 171.

*** Significantly different from zero at the 1% level.

** Significantly different from zero at the 5% level.

* Significantly different from zero at the 10% level.

The results indicate that strong positive relationship between the adult obesity rates and the COVID-19 attributed deaths persists at 5% significance level (or better) for all but the lowest twenty percentile. Countries with lowest mortality rates are also the countries with lowest prevalence of obesity.

The relationship between the share of 65 and older population and the COVID-19 attributed mortality rates is also strong. It is positive and statistically significant at 10 percent significance level (or better) at all but the lowest and highest 10%iles only. This result is consistent with the DAGs established positive causal relationship between the share of 65 and older population and the COVID-19 mortality rates. Finally, no significant correlations at any percentile are observed between the vaccination rate and population density, and the COVID-19 attributed mortality rates. The HDI is negatively correlated, at 10% significance level, only at the 60th percentile with the COVID-19 attributed mortality rates. Hence, direct impact of economic affluence on the mortality due to COVID-19 is all but negligible globally.

Further robustness check

To further check for the robustness of the above results, same analysis is conducted but on the mortality data through November 30, 2020. Therefore, we consider the period prior to the beginning of the COVID-19 vaccination worldwide in December of 2020. While we lose the vaccination control variable here, all other data remains the same with the exception of mortality data. In one final robustness check run, we also substitute the GDP per capita for HDI, as an alternative measure of relative affluence or development. DAGs results are presented in Fig. 4 and related Table 7, Table 8. Panel (a) presents the causal relationships from HDI to the prevalence of adult obesity and percentage of population older than 65, and from those to Covid-19 attributable deaths (per million), accounting for causality from countries’ population density. Panel (b) replicates the model but using GDP per capita instead of HDI. Arrows represent the direction of causality and values on the arrows represent their sign and strength, mean represent the mean of the variables in the model, and E represent their standard deviation. We find positive and statistically significant causalities from the prevalence of adult obesity and percentage of population older than 65 under the two model specifications (see Table 7, Table 8). HDI has an indirect impact on mortality via both obesity and older age.

Fig. 4

Causality between Covid-19 mortality and related comorbidities using Directed Acyclic Graphs under two model specifications-through November, 2022.

Table 7

Statistical results associated with DAG (panel a in Fig. 4).

From	To	Type	Value	SE	Ta	Pa
adult obesity	deaths	Edge Coef.	9.2079	1.9154	4.8072	0.0000
hdi	older65	Edge Coef.	30.2060	2.1589	13.9916	0.0000
older65	deaths	Edge Coef.	4.8548	2.6824	1.8099	0.0722
hdi	adult obesity	Edge Coef.	35.7923	3.5584	10.0587	0.0000
pop_density	deaths	Edge Coef.	-0.0136	0.0242	-0.5618	0.5750

Null hypothesis for T and P is that the parameter is zero.

Table 8

Statistical results associated with DAG (panel b in Fig. 4).

From	To	Type	Value	SE	Ta	Pa
gdp_pc	older65	Edge Coef.	0.0001	0.0000	6.6445	0.0000
adult obesity	deaths	Edge Coef.	9.2079	1.9154	4.8072	0.0000
gdp_pc	adult obesity	Edge Coef.	0.0002	0.0000	6.1545	0.0000
pop_density	deaths	Edge Coef.	-0.0136	0.0242	-0.5618	0.5750
older65	deaths	Edge Coef.	4.8548	2.6824	1.8099	0.0722

Null hypothesis for T and P is that the parameter is zero.

The results of the quantile regression follow and they indicate similar pattern as in the original time-frame: that strong positive relationship between the adult obesity rates and the COVID-19 attributed deaths persists at 1% significance level for all but the lowest ten percentile. Countries with lowest mortality rates are also the countries with lowest prevalence of obesity.

The relationship between the share of 65 and older population and the COVID-19 attributed mortality rates positive and statistically significant at 10% significance level at the 20th, 40th, 60th, 70th and 80th percentiles only, and not significant at other percentiles. This result is again consistent with the DAGs established positive but statistically weak causal relationship between the share of 65 and older population and the COVID-19 mortality rates. The impact of older population on increased COVID-19 attributed mortality rates is established but is not as obvious as the popular narrative seems to imply. Finally, no significant correlations at any percentile are observed between the HDI or GDP per capita and population density, and the COVID-19 attributed mortality rates; hence, these results are not included in Table 9.

Table 9

Results of the quantile regression – period through 11/30/2020.

Quantile/variable	Coefficient	Std. Err	t	P	[95% interval]
q10
Adult obesity	0.488	0.380	1.290	0.200	-0.262	1.238
Older 65	0.665	0.466	1.430	0.155	-0.254	1.585
Constant	-5.819	3.542	-1.640	0.102	-12.811	1.173
q20
Adult obesity	1.612	0.422	3.820	0.000	0.779	2.445
Older 65	1.182	0.625	1.890	0.060	-0.052	2.417
Constant	-14.743	3.823	-3.860	0.000	-22.291	-7.196
q30
Adult obesity	2.301	0.473	4.860	0.000	1.367	3.235
Older 65	1.291	1.540	0.840	0.403	-1.749	4.331
Constant	-16.276	4.184	-3.890	0.000	-24.535	-8.016
q40
Adult obesity	3.809	0.767	4.970	0.000	2.295	5.323
Older 65	3.833	1.901	2.020	0.045	0.081	7.585
Constant	-33.590	5.179	-6.490	0.000	-43.814	-23.366
q50
Adult obesity	5.054	1.568	3.220	0.002	1.959	8.150
Older 65	4.239	2.832	1.500	0.136	-1.352	9.830
Constant	-40.561	7.845	-5.170	0.000	-56.048	-25.074
q60
Adult obesity	6.982	1.670	4.180	0.000	3.685	10.279
Older 65	5.352	3.165	1.690	0.093	-0.895	11.599
Constant	-50.844	9.084	-5.600	0.000	-68.776	-32.913
q70
Adult obesity	9.720	1.589	6.120	0.000	6.584	12.856
Older 65	8.210	3.991	2.060	0.041	0.332	16.088
Constant	-71.215	11.171	-6.380	0.000	-93.266	-49.164
q80
Adult obesity	11.661	1.581	7.380	0.000	8.540	14.781
Older 65	16.923	5.595	3.020	0.003	5.880	27.967
Constant	-102.863	16.767	-6.130	0.000	-135.962	-69.765
q90
Adult obesity	24.578	5.237	4.690	0.000	14.240	34.916
Older 65	9.478	7.258	1.310	0.193	-4.849	23.805
Constant	-119.722	18.862	-6.350	0.000	-156.956	-82.488
Number of cases	173

Policy implications and conclusions

The implications of globalization are different for different countries and regions. Rich, more developed countries are leading the charge and promote the idea of globalization, which enables them to enlarge the markets for their products and increase the socio-political influence on the rest of the world (Croucher, 2018). Many positive aspects of globalization are likely to lead to an increase in standard of living in most countries of the world. Yet, there are some unwanted side-effects of globalization such as the increase in obesity, which is now considered a global epidemic (Miljkovic et al., 2015). Likewise, the impact of globalization on spreading of infectious diseases, including COVID-19, is even more easily observed and measured (e.g., Bickley, Chan, Skali, Stadelmann & Torgler, 2021; Frenk, Gómez-Dantés, & Knaul, 2011; Saker, Lee, Cannito, Gilmore, & Campbell-Lendrum, 2004). Different nature of these global epidemics, i.e., obesity and COVID-19, seems to have triggered different approach of addressing them or a lack thereof at all. The intrinsic link between the two epidemics, as presented in our results, provides an opportunity to remedy this lack of global policy strategy when it comes to obesity.

There is single largest unidirectional causality running from adult obesity to COVID-19 attributed deaths determined globally and present across all percentiles (but the lowest ten percent) of COVID-19 mortality rates. This result holds in the pre-vaccination, early vaccination, and full-vaccination (including boosters) stages of COVID-19 pandemic. This fact creates an opportunity to organize coordinated efforts to address and to remedy the problem on the global level. Such an effort is likely to have best chance of succeeding if organized by a central hub that is a well-respected global public health institution with already existing knowhow in leading similar endeavors. Most obvious candidate for this role would be the WHO. While the WHO has already taken a lead role in prescribing the guidelines for minimizing the risk of spreading and contracting the COVID-19, there is this area of combating global obesity where the WHO could contribute substantially to alleviating the mortality rate attributed to COVID-19 as well as of other related comorbidities. Given that obesity is a non-contagious disease, each country chose to address it based on their own set of health standards as well as cultural values often leading to complete inaction in terms of preventative activities. Unlike obesity, COVID-19 is highly contagious and national borders are not an obstacle for its global spread. Hence global strategy in combating COVID-19 has always been desirable.

As a long-term strategy, the WHO could also assume the leadership in the global fight against obesity, indirectly one of the largest contributors to human mortality due to many comorbidities caused by it including the COVID-19 deaths. Most economic research regarding obesity, thus far, had national focus and specific food policy and health measures. Notably, much of the literature focused on variants of habit formation and addiction theory regarding specific foods and beverages in specific countries (e.g., Miljkovic and Nganje, 2008; Miljkovic, Nganje, & Chastenet, 2008; Thunström, 2010; Zhen, Wohlgenant, Karns, & Kaufman, 2011). Based on these models, the public health impacts of a fat tax (e.g., Jensen & Smed, 2013; Miljkovic et al., 2008) were typically considered for each of the countries.

While there is a recognition among scientists about the ill-effects of obesity on human health globally, food politics and special interest lobbying successes made it unpopular and difficult to fight this problem (Nestle, 2013). The WHO’s status as the world’s leading global public health institution could ensure its credibility and neutrality to provide educational material and counseling that promote healthy nutrition and lifestyle even in nations where food industry special interests overwrite national public health and social welfare priorities. Another obstacle in the way of making reducing obesity number one public health priority globally in the long run is an emphasis of the WHO and the Food and Agriculture Organization of the United Nations on food security, malnutrition and hunger. Both prevention and reduction of postharvest losses and advancements in biotechnology ensure enough food supply globally (Miljkovic & Winter-Nelson, 2021), thus making food security, unlike obesity, a political rather than public health issue (e.g., Kennedy, 2018; Miljkovic, 2015).

Media coverage and public perceptions have been centered on the presence of seemingly efficient and safe COVID-19 vaccines. Yet, our results suggest no direct causal relationship between COVID-19 vaccination rate and deaths attributed to COVID-19. Moreover, quantile regression results indicate that for no sample (quantile) of countries, from those with the lowest to those with the highest mortality rates attributed to COVID-19 does the vaccination rate have any impact on death from COVID-19. Only indirectly vaccination may have an impact on lesser mortality from COVID-19 as there is no direct causal link between the population of 65 and older who received booster shot, and the mortality rate from COVID-19. Obesity, however, remains largest contributor to mortality from COVID-19 in all considered cases. While our results point to obesity as the largest and most persistent contributors to mortality from COVID-19, all global and national public health efforts seem to be directed into intensifying vaccination rate while no efforts are made to address obesity and related comorbidities as at least long-term target variables.

In conclusion, comorbidities associated with obesity are same as many attributed to COVID-19 deaths. Most important finding is that obese population is identified as most-at-risk if infected by COVID-19. In turn, this finding underlines the need for centralized long-term strategy and leadership in fighting global obesity as the largest long-lasting global public health issue.

Table A1

List of countries within the sample of the study. Dataset contains data on 171 countries, accounting for 98.2% of the global population in 2020.

Afghanistan	Canada	Gabon	Laos	Nigeria	Spain
Albania	Cape Verde	Gambia	Latvia	North Macedonia	Sri Lanka
Algeria	Central African Republic	Georgia	Lebanon	Norway	Suriname
Angola	Chad	Germany	Lesotho	Oman	Sweden
Antigua and Barbuda	Chile	Ghana	Liberia	Pakistan	Switzerland
Argentina	China	Greece	Libya	Panama	Tajikistan
Armenia	Colombia	Grenada	Lithuania	Papua New Guinea	Tanzania
Australia	Comoros	Guatemala	Luxembourg	Paraguay	Thailand
Austria	Congo	Guinea	Madagascar	Peru	Timor
Azerbaijan	Costa Rica	Guinea-Bissau	Malawi	Philippines	Togo
Bahamas	Cote d′Ivoire	Guyana	Malaysia	Poland	Trinidad and Tobago
Bahrain	Croatia	Haiti	Maldives	Portugal	Tunisia
Bangladesh	Cyprus	Honduras	Mali	Qatar	Turkey
Barbados	Czechia	Hungary	Malta	Romania	Uganda
Belarus	Denmark	Iceland	Mauritania	Russia	Ukraine
Belgium	Djibouti	India	Mauritius	Rwanda	United Arab Emirates
Belize	Dominican Republic	Indonesia	Mexico	Saint Lucia	United Kingdom
Benin	DR of Congo	Iran	Moldova	Saint Vincent	United States
Bhutan	Ecuador	Iraq	Mongolia	Sao Tome and Principe	Uruguay
Bolivia	Egypt	Ireland	Montenegro	Saudi Arabia	Uzbekistan
Bosnia and Herzegovina	El Salvador	Israel	Morocco	Senegal	Vanuatu
Botswana	Equatorial Guinea	Italy	Mozambique	Serbia	Venezuela
Brazil	Eritrea	Jamaica	Myanmar	Seychelles	Vietnam
Brunei	Estonia	Japan	Namibia	Sierra Leone	Yemen
Bulgaria	Eswatini	Jordan	Nepal	Singapore	Zambia
Burkina Faso	Ethiopia	Kazakhstan	Netherlands	Slovakia	Zimbabwe
Burundi	Fiji	Kenya	New Zealand	Slovenia
Cambodia	Finland	Kuwait	Nicaragua	South Africa
Cameroon	France	Kyrgyzstan	Niger	South Korea