Low cardiorespiratory fitness has been established as a risk factor for cardiovascular-related morbidity. However, research about the impact of fitness on lipid abnormalities, including atherogenic dyslipidemia, has produced mixed results. The purpose of this investigation is to examine the influence of baseline fitness and changes in fitness on the development of atherogenic dyslipidemia.
Methods
All participants completed at least 3 comprehensive medical examinations performed by a physician that included a maximal treadmill test between 1976 and 2006 at the Cooper Clinic in Dallas, Texas. Atherogenic dyslipidemia was defined as a triad of lipid abnormalities: low high-density-lipoprotein cholesterol ([HDL-C] <40 mg/dL), high triglycerides ([TGs] ≥200 mg/dL), and high low-density-lipoprotein cholesterol ([LDL-C] ≥160 mg/dL).
Results
A total of 193 participants developed atherogenic dyslipidemia during an average of 8.85 years of follow-up. High baseline fitness was protective against the development of atherogenic dyslipidemia in comparison with those with low fitness (odds ratio [OR] 0.57; 95% confidence interval [CI], 0.37-0.89); however, this relationship became nonsignificant after controlling for baseline HDL-C, LDL-C, and TG levels. Participants who maintained fitness over time had lower odds of developing atherogenic dyslipidemia than those with a reduction in fitness (OR 0.56; 95% CI, 0.34-0.91) after adjusting for baseline confounders and changes in known risk factors.
Conclusions
High fitness at baseline and maintenance of fitness over time are protective against the development of atherogenic dyslipidemia.
Epidemiological studies consistently demonstrate the independent effects of lipid abnormalities as risk factors for cardiovascular disease in populations worldwide. In the US, about half of the adult population has at least one lipid abnormality, and about 6% have a triad of lipid abnormalities. The lipid triad, also known as atherogenic dyslipidemia, consists of a combination of elevated low-density-lipoprotein cholesterol (LDL-C), reduced levels of high-density-lipoprotein cholesterol (HDL-C), and elevated triglycerides (TGs). In addition to the independent effects, the presence of the lipid triad, as a whole, is considered a strong independent risk factor for cardiovascular disease.
Between 1988 and 1994, there was a sixfold increase in US adults aged 18 to 64 years who were prescribed cholesterol-lowering medication, and almost half (46.7%) of Americans over the age of 65 years reported taking cholesterol-lowering medication within the previous 30 days. Pharmacotherapy in conjugation with lifestyle modification is strongly promoted, and this multifactorial approach targets several lifestyle behaviors, including physical inactivity and poor dietary patterns, each with known impacts on lipid abnormalities.
The literature indicates that regular exercise elicits significant improvements to TG, total cholesterol, and HDL-C levels, whereas LDL-C is largely unaffected by regular exercise when body weight and diet remain unchanged. In addition to exercise, cardiorespiratory fitness (hereafter referred to as fitness)—an objective indicator of habitual physical activity and a strong predictor for cardiovascular disease-related outcomes—is associated with lipid abnormalities. There is evidence suggesting that higher levels of baseline fitness are positively associated with plasma levels of HDL-C, as well as with lower odds of developing incident hypercholesterolemia.
In addition to baseline fitness levels, the impact of fitness changes over time on plasma lipid concentrations have also been examined, but the results are mixed. Some investigators have observed no associations between changes in fitness levels following an exercise intervention and changes in the individual components of the lipid triad. Whereas other studies have observed significant correlations between changes in fitness levels and changes in total cholesterol, HDL-C, and TG levels. Additionally, maintaining or improving fitness levels over time is associated with a lower risk for elevated total cholesterol in adults.
Although the findings are mixed, the overall trend demonstrates that the greatest improvements to plasma cholesterol levels are more likely to occur among individuals who have greater increases in fitness post intervention. However, the literature has focused primarily on the individual components of the lipid triad. Therefore, the purpose of this present study was to examine the association between baseline fitness levels and changes in fitness levels on the odds of developing atherogenic dyslipidemia in adults using data from the Aerobics Center Longitudinal Study (ACLS).
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-Charity B. Breneman, MS, MSPH, Kristen Polinski, MSPH, Mark A. Sarzynski, PhD, Carl J. Lavie, MD, Peter F. Kokkinos, PhD, Ali Ahmed, MD, MPH, Xuemei Sui, MD, MPH, PhD
This article originally appeared in the October 2016 issue of The American Journal of Medicine.
