Comorbidities of overweight and obesity: current evidence and research issues.

PURPOSE: The evidence with regard to the relationship of obesity with medical comorbidities was assessed and priority research issues identified.
METHODS: The existing literature in English was surveyed.
RESULTS: The evidence is overwhelming on the association of obesity to a number of medical conditions. These include: insulin resistance, glucose intolerance, diabetes mellitus, hypertension, dyslipidemia, sleep apnea, arthritis, hyperuricemia, gall bladder disease, and certain types of cancer. The independent association of obesity seems also clearly established for coronary artery disease, heart failure, cardiac arrhythmia, stroke, and menstrual irregularities. The relationship between central (or upper body) obesity and the above conditions is positive for most of them but with a lesser number of studies. Most of the fat distribution studies have been done using anthropometric measurements rather than the more accurate magnetic resonance imaging or computer tomographic scans. Priority research issues include the following: more definitive data on the relation of central fat to comorbidities; the proportional importance of subcutaneous versus visceral fat in producing comorbidities; the relationship between obesity and psychiatric disease; the genetics of the relationship between obesity and each of the comorbidities; the independent contribution of diet and of sedentariness to the development of each of the comorbidities; the impact of gender, race, intensity, and duration on these associations.
CONCLUSIONS: The evidence for the relationship of obesity to a number of comorbidities is strong, though the strength of the relationship varies with the condition. Much more research is necessary on causation and on what other factors may play an interactive role.