People who exercise more show fewer signs of a major metabolic disturbance associated with HIV therapy – elevated triglyceride levels - according to a study of 120 HIV-positive patients at Boston’s Beth Israel Medical Centre, published this week in the June 15th edition of Clinical Infectious Diseases.
The study was designed to investigate whether exercise and diet affected the development of lipodystrophy and metabolic disorders in people who had been exposed to highly active antiretroviral therapy for at least six months.
Dietary factors known to be associated with the metabolic syndrome in HIV-negative people, such as low consumption of free fatty acids, fibre, monosaturated fats and vitamin E were evaluated by means of a food questionnaire, and patients were tested for plasma levels of cholesterol, triglycerides and fasting glucose. Whole body fat was measured using a DEXA scan, whilst central fat distribution was measured using a CT scan.
Exercise levels were evaluated according to type of exercise, its frequency and the duration. Walking and swimming were classified as light exercise (level 1). Running, use of exercise machines or aerobic exercise were classified as moderate activity (level 2), and weight training as heavy activity (level 3). Activity was also divided between aerobic and other exercise, and cumulative indices were calculated for each by multiplying the number of sessions by the duration in minutes, and then multiplying by the intensity category (1,2 or 3).
The study was cross-sectional, so the duration of antiretroviral therapy for patients recruited to the study was variable. The mean duration of protease inhibitor exposure was 41 months in the lipodystrophy group versus 31 months in the non-lipodystrophic group. Nucleoside analogue exposure was significantly greater in the lipodystrophy group (136 vs 96 months), and amongst those with lipodystrophy, exposure was significantly greater among those whose syndrome included fat wasting than those who developed fat accumulation (p
Sixty nine patients had signs of fat redistribution on entry to the study, 23 of whom had lipoatrophy only, 17 central fat accumulation only and 29 a mixture of the two. Those with the mixed form of fat redistribution were significantly older, had significantly greater duration of PI and NRTI exposure than non-lipodystrophic individuals (42 vs 31 months, p=0.008; 148 vs 96 months, p
Those with fat wasting did not differ from the non-lipodystrophic patients in terms of PI exposure, total or LDL cholesterol, but did have greater NRTI exposure, higher triglyceride levels and lower HDL cholesterol. No differences in viral load or CD4 count were evident between any of the groups.
Insulin resistance was significantly greater among those with a mixed lipodystrophy syndrome or fat loss than people without.
Multivariate analysis showed that triglyceride levels were negatively associated with total exercise (as calculated by the formula above) (p=0.004), but a similar association was not found for LDL, HDL or total cholesterol, nor for insulin resistance. Triglyceride levels were not associated with lean body mass, suggesting to the authors that the mechanism by which exercise promotes lower triglyceride levels in this group of patients is not the greater muscle mass available to remove triglycerides from the circulation. Instead they suggest that increased lipoprotein lipase expression in muscle tissue after exercise is stimulating the release of free fatty acids from plasma lipoproteins, in order to replenish intramuscular triglyceride supplies after exercise.
Individuals with fat wasting had significantly greater exercise scores than individuals with mixed fat redistribution or fat accumulation.
Vitamin E intake, both in food and supplement form, was inversely associated with diastolic blood pressure and both total body fat and subcutaneous abdominal fat percentage (p=0.003, 0.004). This may have been a partial consequence of the high calorie intake reported by those with fat wasting, which was significantly greater than any other group's consumption.
Dietary fat intake, whether polunsaturated, saturated or monounsaturated, did not affect serum lipid levels.
Gavrila A et al. Exercise and vitamin E intake are independently associated with metabolic abnormalities in human immunodeficiency virus-positive subjects: a cross-sectional study. Clinical Infectious Diseases 36: 1593-1601, 2003.