Seasonal Changes Could Alter Cholesterol Levels

Seasonal Changes Could Alter Cholesterol Levels

According to recent research published in the [u]Archives of Internal Medicine[/u], cholesterol levels may vary according to the seasons. Over 500 healthy volunteers around the central Massachusetts area participated in this study, and their cholesterol levels were analyzed quarterly over a year. In addition to a total cholesterol workup, the volunteers were required to report their diet, amount of time they were exposed to sunlight, behavioral information, and their physical activity during this time.

Researchers discovered that cholesterol levels were highest during the winter months and lowest during the summer months. The average total cholesterol level among the participants was 222 mg/dL in men and 213 mg/dL in women. During the winter months, cholesterol levels were increased in men and women by 3.9 mg/dL and 5.4 mg/dL respectively, with the men’s total cholesterol levels being the highest in December, and the women’s total cholesterol levels being the highest in January. The average total cholesterol levels in both of the men and women are considered borderline high by guidelines set forth by the National Cholesterol Education Program (NCEP), and the authors of the paper remark that the increases in cholesterol found in the winter months were greater in those who already had high cholesterol levels and in women. Additionally, 22% more participants had total cholesterol levels over 240 mg/dL during the winter months which, according to the NCEP guidelines, are considered high.

Why does such a variation exist? The mechanism is uncertain. However, such a variation in total cholesterol levels could lead to more individuals being diagnosed with high cholesterol during the winter months as opposed the summer months. There were no statistically significant variations between seasons and the diet of the participants. Previous studies have indicated that relative plasma volume, where cholesterol is located in the blood, changes with the seasons, and this could also involve cholesterol levels. Additonally, there is a question as to whether or not physical activity plays a role with this mystery. Physical activity is usually greatest during the summer months and lowest during the winter months, and increased physical activity does play an important role in lowering cholesterol levels.

The authors are not proposing changes to the guidelines regarding this seasonal data until more research is performed to further explore this phenomenon and determine a mechanism by which this occurs.


<sub>Sources:

Third Report of the National Cholesterol Education Program (NCEP) Expert Panel on Detection, Evaluation, and Treatment of High Blood Cholesterol in Adults (PDF), July 2004, The National Institutes of Heath: The National Heart, Lung, and Blood Institute.

Ockene IS et al. Seasonal variation in serum cholesterol levels: treatment implications and possible mechanisms. Arch Intern Med. 2004 Apr 26;164(8):863-70.</sub>