In a cohort of male physicians with measurements of HDL-C 14 years apart, the authors found that stable low BMI, decreasing BMI, moderate alcohol consumption, and increasing alcohol consumption were all associated with increases in HDL-C, while decreases in physical activity were associated with decreases in HDL-C. In analyses examining potential interactions between baseline HDL-C and lifestyle changes and analyses stratified by baseline HDL-C both demonstrated that the effect of some lifestyle changes, such as becoming sedentary, on HDL-C change varied according to baseline HDL-C.
In this study, the magnitude of HDL-C increase associated with weight loss, maintaining low BMI, maintaining moderate alcohol intake, or increasing alcohol intake varied between approximately 5 and 10%, corroborating previous studies that examined associations between these lifestyle factors and HDL-C (1
). Unlike previous cross-sectional studies examining associations between exercise and HDL-C, these authors did not find an association between increases in physical activity and changes in HDL-C(1
). These findings may reflect the fact that most subjects (54.7%) were regularly physically active over the entire 14-year period, so HDL-C response to increases or decreases in physical activity in the small number of subjects who experienced them may not have been detected.
The authors identified a subgroup of n=554 subjects who achieved an increase in HDL-C of ≥12.5 mg/dL during follow-up. There are several potential explanations why these men may have had their large increases in HDL-C. CMT use was initiated in 26.0% of this subgroup during the study period. Many of these men may have made favorable lifestyle changes simultaneously, such as reducing BMI, as reflected in . These 554 men were older and more likely to have baseline hypertension and diabetes, which may have provided impetus for these and additional, unmeasured lifestyle changes (diet, for instance) to promote higher HDL-C. Alternatively, this group may represent “strong responders” in whom genetic factors may be responsible for these larger HDL-C increases that resulted from lifestyle changes. Previous authors examining whether genes modify the impact of lifestyle on HDL-C levels have had mixed results (18
Updated lifestyle parameters over time and 2 available measurements of HDL-C levels taken 14 years apart PHS I make this cohort ideal for examining associations between changes in lifestyle parameters and changes in lipids. However, some limitations should be noted. First, this study was underpowered to evaluate the impact of smaller incremental changes in lifestyle factors (such as increasing from weekly to daily exercise) on HDL-C change. Using the broad definitions of changes in lifestyle used here, the analysis had a power of ≥80% to detect an HDL-C increase of 5% for many the activity, BMI, and alcohol consumption category comparisons. Although a large number of subjects (626) had missing data regarding baseline CMT use, a small number of men for whom baseline CMT use was available used CMT (5
), so it is unlikely that missing baseline CMT data could have biased our findings. We did not examine lifestyle impact on HDL-C subclasses as this data is available on a small number of PHS participants; examining whether lifestyle variably impacts HDL-C subclasses represents a potentially important area of future research (19
). We did not find significant associations between race and HDL-C change, however the number of non-white participants in PHS is very small. Examining associations between lifestyle changes and HDL-C change in persons of varying racial background, in women, in persons of varying geographic background, or subjects with known co morbidities such as heart disease, represents an important area of future research. Residual confounding, such as the impact of fluctuating dietary factors on HDL-C change, may be a concern and remains an area of important future research.
Sources of variation in our measurement of HDL-C change for which we could not account include regression to the mean, within-individual variation, differences in laboratory technique, or other unobserved predictors of HDL-C (20
). We would expect, however, that these sources of measurement error would impact the sample in a uniform fashion and thus influence our results toward the null. Thus the magnitude of significant lifestyle-HDL-C change associations that we found is likely to be underestimated in this study.
This study demonstrates that adopting or maintaining favorable lifestyle habits are associated with increases HDL-C, while adopting or maintaining unfavorable may result in decreases in HDL-C over time in a cohort of male physicians. Although more questions regarding the relationships between lifestyle modification and HDL-C change remain, our results provide further support for the promotion of maintaining a low BMI, pursuing a physically active lifestyle, and other beneficial lifestyle factors.