Case Study: Aerobic Exercise and the Effects on Triglycerides for the Purpose of Cardiovascular Risk Reduction

Introduction
Elevated triglycerides alter lipoprotein metabolism thus should be considered an independent risk factor for cardiovascular disease mortality. Altered lipoprotein metabolism can result in elevated plasma lipids; one of the seven major risk factors for cardiovascular mortality (along with smoking, obesity, hypertension, diabetes, low physical activity, and abundant alcohol intake).¹ This case study will focus on the reduction of elevated triglycerides into normal range and how it can reduce the risk of Cardiovascular Disease, CVD, mortality. Treatment options for elevated triglycerides include pharmaceuticals or lifestyle modification.² Pharmaceutical intervention should be decided upon by physicians based on current plasma levels, risk of a cardiovascular event, presence of CVD, as well as the other risk factors. For those with only mild to moderate lipid plasma elevation, many physicians start with prescribing lifestyle modifications. Lifestyle modifications specifically for triglyceride reduction include weight loss if indicated, diet optimization, avoidance of alcohol, and an increase in physical activity.³ When pursuing physical activity for triglyceride reduction, aerobic endurance exercise should be the preferred recommendation, for both a single session as well as habitual exercise, are known to lower plasma triglyceride concentrations.⁴

Plasma triglyceride reductions are achieved through aerobic exercise from the decrease in hepatic triglycerides and very-low-density lipoprotein (VLDL) synthesis and secretion.⁵ These decreases paired with an increase in muscle lipoprotein lipase activity result in lowered triglycerides. The reductions in triglycerides are often observed after endurance exercise sessions similar to those characterized to increase high-density lipoprotein cholesterol, HDL-C which has known cardiovascular benefits.⁴ Studies suggest a dose–response relationship between increases in physical activity and improvements in triglycerides and HDL cholesterol in previously sedentary populations.⁶ Meanwhile, aerobic exercise resulting in reduced body fat or weight, has been shown to lower total cholesterol and low-density-lipoprotein cholesterol (LDL-C) concentrations, further increasing the cardiovascular benefits of aerobic exercise on lipid management.⁴

Aerobic exercise is loosely defined as physical activity that increases the heart rate and body’s use of oxygen. This definition leaves room for interpretation, specifically the amount of increase in heart rate, or the intensity. To achieve the desired dose-response between physical activity and triglyceride improvement, intensity of exercise should be controlled. This is best done by prescribing heart rate zones based on percent maximal oxygen consumption, or VO₂ max. VO₂ max is assessed through a VO₂ max test with heart rate monitoring and gas analysis, the gold standard of cardiorespiratory fitness testing. Studies show exercising at a heart rate correlated to 65-80% VO₂ max, is best for lipid management.⁷

Case Presentation
The patient is a 66-year-old Caucasian male with no known acute or chronic diseases other than dyslipidemia, hypertension, and being overweight. He has no surgical history. He presented to his cardiologist for his annual exam as asymptomatic and denied any recent changes in weight or appetite. He has a strong family history of CVD. He currently takes no medication. He disclosed drinking 1-2, 5 oz glasses of red wine, 4-5 days per week and reported never smoking.

Treatment
The patient was referred to an exercise physiologist for exercise guidance. A cardiovascular risk assessment was performed by his cardiologist which showed three main risks: his elevated LDLs, elevated triglycerides, as well as strong family history of CVD. Though eligible, he wanted to avoid pharmaceutical intervention. Due to having only mild elevations, he was cleared to begin with lifestyle modifications. He reported playing sports while young but lived a sedentary lifestyle in adulthood. Time was not a limitation, though he expressed hesitancy in finding motivation for exercise that required strenuous exertion or required equipment. He underwent VO₂ max testing to determine the best intensity of exercise for lipid management. Per the results of his VO₂ max test he was instructed to sustain a heart rate of 90-115 bpm which translated to 65-80% of his VO₂ max for a total of 150 minutes per week. Sessions were to last 10 to 60 minutes per session and could be performed in his preferred modality of exercise. 

An overview of his pre- and post-exercise program laboratory results can be found in Table 1.

Four months after his initial visit, he reported adherence to the exercise plan having achieved 150 minutes 11 out of 12 weeks. He began the program with shorter walks, 10 to 15 minutes, multiple times per day and increased the session time to walking 45 minutes over the 12 weeks. Exercise sessions were completed primarily outdoors in his neighborhood and occasionally on a treadmill in the case of inclement weather. The heart rates were adhered to using a Fitbit with heart rate capability. He also reported improved mental health and sleep benefits from being outdoors in fresh air. And, he began to look forward to walks as a stress relieving tool. No dietary interventions or changes were made during this period. His lipid panel showed the following improvements: triglycerides decreased from 166.9 to 138.5 mg/dL, p<0.05; LDL cholesterol decreased from 130.1 to 128.2 mg/dL, p<0.05; HDL cholesterol increased from 44.3 to 48.6 mg/dL, p<0.05.

Discussion
Elevated triglycerides can be considered an independent risk factor for cardiovascular disease and can be managed through lifestyle modifications. These lifestyle modifications should only be recommended after a risk assessment has been performed and the patient has been cleared to exercise. When treating patients with mild to moderate elevated triglycerides, aerobic exercise should be one of the initial recommendations. The gold standard would be to recommend VO₂ max testing and provide heart rate zones that correspond to 65-80% VO₂ max. VO₂ max testing requires exercise testing equipment and trained staff, which are cost prohibitive. In the instances where testing is not feasible, maintaining moderate exercise, where a conversation can be maintained with some effort should be recommended for a total of 150 minutes per week. Modality of exercise (walking, swimming, biking, etc.) can be based on the patient’s preference to promote adherence to the program. The only requirement is the modality must be able to maintain an elevated heart rate for sustained periods of time.

The reduction in cardiovascular risk factors is maximized with adherence to regular exercise recommendations. To increase adherence, patients can work with exercise physiologists to address and overcome barriers to exercise such as time, access to equipment, or low motivation. Often after regular adherence to exercise, patients find making diet changes more approachable. Dietary approaches have been proven successful in reducing not only triglycerides, but also LDL-C and total cholesterol further. Simultaneous diet and exercise optimization is a great opportunity to maximize reduction in cardiovascular risk factor through lifestyle modifications.

Disclosure statement: Ms. Bannister has no financial disclosures to report.
References are listed in the 2022 spring Lipidspin .pdf on www.lipid.org