Frequent intentional weight loss is associated with lower natural killer cell cytotoxicity in postmenopausal women: possible long-term immune effects.

OBJECTIVE: Weight-loss attempts are likely to become more frequent as the prevalence of obesity rises. Repeated cycles of loss and gain are a common consequence of failed weight-loss attempts. The question of whether this pattern has negative health effects is unresolved. The objective of this research was to investigate associations between weight-loss history and current measures of immune function.
DESIGN: The study design was a cross-sectional study.
SUBJECTS: One hundred fourteen healthy, overweight, sedentary, postmenopausal women were recruited for an exercise intervention study and were currently weight stable.
METHODS: History of intentional weight loss was assessed by questionnaire. Flow cytometry was used to measure natural killer cell (NK) cytotoxicity at four effector-to-target (E:T) ratios and for enumerating and phenotyping lymphocytes. Multiple linear regression analysis was used to investigate associations between weight loss within the past 20 years and current immune function.
RESULTS: Women who reported ever intentionally losing >or=10 pounds had lower measured NK cytotoxicity than those who did not (24.7%+/-12.1% vs 31.1%+/-14.7%, respectively, at E:T 25:1; P=.01). Increasing frequency of previous intentional weight loss was associated with lower NK cytotoxicity (P=.003, trend). As an independent predictor, longer duration of recent weight stability was associated with higher NK cytotoxicity (21.6%+/-11.9%, 24.4%+/-11.0%, and 31.9%+/-14.4% for <or=2, >2 to <or=5, and >5 years of weight stability, respectively; P=.0002, trend). The frequency of weight loss episodes was also associated with differences in the number and proportion of NK cells.
CONCLUSIONS: This study provides evidence that frequent intentional weight loss may have long-term effects on immune function.