Favourable changes in HDL cholesterol and triglyceride levels: Framingham analysis

Data from the Framingham Offspring Study suggest improvements in dyslipidemia, notably an increase in high density lipoprotein (HDL) cholesterol and decrease in triglycerides over the period 1991-2001. This was despite an overall increase in body mass index (BMI).  The data were reviewed by HDL Forum Editor Kerry-Anne Rye.

 

Ingelsson E, Massaro JM, Sutherland P et al. Contemporary trends in dyslipidemia in the Framingham Heart Study. Arch Intern Med 2009;169:279-86.

 

The Framingham Offspring study is a longitudinal study in a second generation sample of Framingham men and women in middle age. In this report, lipid and BMI data from subjects who attended examinations in 1991-1994, 1995-1998 and 1998-2001 were evaluated.

 

The main analysis included 1,666 subjects (56% men) without cardiovascular disease and who were not prescribed lipid and/or hormone therapy during this period While total cholesterol did not change significantly in men or women, HDL cholesterol levels increased (multivariate adjusted mean values: 44.4 to 46.6 mg/dL in men and 56.9 to 60.1 mg/dL in women, p<0.001 for trend in both sexes) and triglycerides declined (144.5 to 134.1 mg/dL in men, p=00.4 and 122.3 to 112.3 mg/dL in women, p<0.001) (Table 1). Interestingly, this was despite a significant increase in body mass (from 27.8 to 28.5 kg/m2, p<0.001 for men, and 27.0 to 27.6 g/m2, p=0.001 for women).

 

Table 1. Change in fasting lipid levels, 1991-2001

 

When subjects were grouped according to the pattern of change in lipid levels, the largest category for both men and women was the combination of an increase in HDL cholesterol and decrease in triglycerides (39% of men and 37% of women). These subjects also had the smallest increases in BMI between 1991 and 2001.

 

These findings contrasted to previous reports from the US National Health and Nutrition Examination Survey (NHANES) which reported no significant change in levels of HDL and triglycerides from 1988 to 2002, despite increasing obesity.(1) The authors of the current report suggested that this may have been due to the cross-sectional study design of NHANES.

 

While the authors have no clear explanation for these beneficial changes in lipid levels in a substantial proportion (over one-third) of subjects, they did speculate that changes in the pattern of food consumption in the US, notably increased consumption of carbohydrates and decreased consumption of fats especially saturated fats, suggested by dietary surveys,(2) may be a contributory factor.

 

According to senior author Dr Sander Robins, Boston University School of Medicine, Boston, Massachusetts, this may result in plasma triglyceride-rich lipoproteins with both phospholipids and triglycerides that have more unsaturated acyl groups, making them more susceptible to hydrolysis by lipoprotein lipase. This generates an excess of surface constituents (phospholipids, unesterified cholesterol and apolipoproteins) on the triglyceride-rich lipoprotein surface that can transfer to pre-existing HDL particles that increase in size (Fig 2a).

 

 

Alternatively these may be converted into new discoidal HDL particles that are converted into spherical HDL by LCAT (Fig 2b).

 

However, further studies investigating specific changes in dietary fat are needed to substantiate this theory.

 

 

References

1. Okosun IS, Chandra KM, Boev A et al. Abdominal adiposity in U.S. adults: prevalence and trends, 1960-2000. Prev Med 2004;39:197-206.

2. Trends in Intake of Energy and Macronutrients --- United States, 1971—2000. Available from http://www.cdc.gov/mmwr/PDF/wk/mm5304.pdf

 


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