SAN FRANCISCO – Cholesterol levels fluctuated significantly by season in a prospective study of 227,359 Brazilians.
Compared with lipid levels in the summer, in the winter the mean plasma LDL cholesterol level increased by 7 mg/dL, resulting in an 8% increase in the prevalence of high LDL cholesterol (>130 mg/dL) in the winter, Dr. Filipe A. Moura and his associates reported at the annual meeting of the American College of Cardiology.
The variations are pronounced enough that clinicians may want to keep a closer eye on patients who are borderline hypercholesterolemic in the summer months, because they may be at higher risk than expected once winter comes, said Dr. Moura, a doctoral candidate at the State University of Campinas, Brazil. He and his associates plan to study patients who present with an MI to see if lipid profiles at presentation vary seasonally in a similar fashion.
The current cross-sectional study prospectively compared lipid levels in patients seen for health checkups in five primary care centers in Campinas from 2008 to 2010. The variations between maximum and minimum lipid levels reached 7 mg/dL for LDL cholesterol, 3 mg/dL for HDL, and 12 mg/dL for triglycerides.
Even greater variations might be seen in nontropical countries that experience more extreme climate changes between seasons, such as the United States or Europe, Dr. Moura speculated. Campinas has mild, dry winters and is located at 1,821-2,559 feet above sea level.
Other lipid levels varied as well. Mean HDL cholesterol levels below 40 mg/dL were 9% more prevalent in summer than in winter, and mean triglyceride levels higher than 150 mg/dL were 5% more prevalent in summer than in winter,
Previous, smaller studies had suggested that there might be seasonal variations in LDL cholesterol. Those studies did not find the increased rates of low HDL and high triglycerides in summer seen in the current study, perhaps because they were not done in tropical climates, he said.
The current study found more pronounced seasonal lipid changes in women and middle-aged adults, but this is likely due to larger sample sizes in these subgroups, Dr. Moura said. Patients ranged in age from less than 1 year to 110 years old, and 64% were female.
Besides the seasonal climate changes, seasonal behavior changes may have affected lipid levels, he speculated. In winter, people tend to exercise less and eat more food in general and fattier foods in particular. Less exposure to sunshine in winter may lower serum concentrations of vitamin D, and vitamin D status has been associated with the ratio of bad to good cholesterol.
Dr. Moura reported having no financial disclosures.