Maintaining cardiorespiratory fitness through early adulthood and midlife delayed unfavorable elevations in blood cholesterol for a group of men whose fitness and overall health was studied over time.
“Strong evidence exists that physical activity is a major modifiable lifestyle factor for preventing dyslipidemia,” said study author Dr. Yong-Moon Mark Park of the University of South Carolina, Columbia and his associates. They used data from the large Aerobics Center Longitudinal Study (ACLS) to characterize age-related changes in the serum lipid profile and to determine whether cardiorespiratory fitness (CRF) might alter the trajectory of change through the lifespan (J. Am. Coll. Cardiol. 2015;65:2091-100 [doi:10.1016/j.jacc.2015.03.517]).
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Assessing the relationship between CRF and blood lipid levels has potentially large clinical and public health significance, since “age-related changes in lipid and lipoprotein concentrations are overall unfavorable,” noted Dr. Park and his associates.
Ordinarily, levels of total cholesterol (TC), LDL cholesterol (LDL-C), and triglycerides (TG) tend to rise over time through middle age and then decrease. The overall pattern of change shows an inverted U shape, with the highest levels occurring at the end of midlife. HDL cholesterol (HDL-C) does not have a consistent pattern of change over time. Previous studies, including robust meta-analyses, have shown that aerobic activity reduces both LDL-C and non HDL-C, but the interplay between CRF and the normal age-related trajectory of blood lipids had not been well understood.
To characterize how CRF affects potentially harmful serum lipid and lipoprotein levels, investigators were able to draw on the ACLS data. This study has been accumulating demographic, lifestyle, medical, and fitness information for a large group of men since 1970.
The ACLS included a thorough assessment of clinical and lifestyle variables, including fasting lipid and glucose levels, blood pressure, body mass index and waist circumference calculation, and body fat calculation. Questionnaires tracked information about physical activity, smoking status, and alcohol use and included an extensive battery of medical history questions.
A modified peak exertion exercise treadmill test, with treadmill time expressed in metabolic equivalents, was used to assess CRF. The analysis standardized CRF for age strata and categorized subjects into low, middle, and high levels of fitness by tertile.
Final analysis included 11,418 men aged at least 20 years who completed at least two examinations and for whom complete study data were available.
Extensive and sophisticated statistical techniques accounted for the many covariates that varied over time, including blood pressure, body fat, waist circumference, and lifestyle factors. A sensitivity analysis was conducted to account for the effect of diabetes or widely varying dietary habits on blood lipid trajectories.
Men with the lowest levels of CRF tended to develop an abnormal lipid profile by as early as their mid-20s until their late 30s. This represented a shift of about 15 years from the age trends of those with the highest levels of CRF. Higher CRF was significantly associated with lower TC, LDL-C, TG, and non–HDL-C and with higher HDL-C, and lower CRF was associated with higher values of all serum lipid markers (all P < 0.0001).
Overall, Dr. Park and his associates said, CRF had a significant effect on the trajectory of change in blood lipid levels over time. “Specifically, CRF was consistently a protective factor for abnormal lipid and lipoprotein profiles, and this prominent effect most frequently appeared between the age of early 20s and early 60s for TC, LDL-C, and non–HDL-C, and between the age of early 20s and early 70s for TG and HDL-C.”
A major limitation of this study was that it included only men. Additionally, participants were over 95% non-Hispanic white, were mostly college graduates, and were of relatively high socioeconomic status. No information about lipid-lowering medication was available, though the authors attempted to control for this lack of data by excluding those with dyslipidemia or known cardiovascular disease at enrollment and follow-up.
The clear association of higher levels of CRF with a delayed elevation of the blood lipid profile shows that “promoting CRF may contribute to a possible delay of dyslipidemia and its related atherosclerosis and CVD,” said Dr. Park and his coworkers.
The study was supported by the National Institutes of Health. One of the investigators is a member of the advisory boards of Technogym, Santech, and Clarity; has received unrestricted research grants from the Coca-Cola Company, Technogym, and BodyMedia; and has received book royalties from Human Kinetics. The other investigators reported having no conflicts of interest.