LDL Cholesterol Levels Lower in Summer, Higher in Winter

The emergence of summer after a long winter appears to have a positive effect on lipid levels, a new analysis has shown. On-treatment LDL-cholesterol levels, regardless of the intensity of statin therapy, are significantly lower in summer than in winter, report investigators.

Dr Patricia Tung, Brigham and Women’s Hospital, Boston, MA, stated that,  “Although this analysis did not examine seasonal differences in adverse events, increases in LDL cholesterol may be important in clinical practice…. For example, if a patient is only slightly lower than a treatment goal in summer, they are likely to be higher than goal in winter, and consideration may be given to intensification of therapy.”

The results are from an analysis of the Pravastatin or Atorvastatin Evaluation and Infection Therapy-Thrombolysis in Myocardial Infarction 22 (PROVE IT-TIMI 22) study, a trial evaluating intensive therapy with atorvastatin 80 mg and moderate therapy with pravastatin 40 mg in 4,162 patients with acute coronary syndrome (ACS).

Previous studies have shown that myocardial ischemic events occur more frequently in winter than in summer, and other longitudinal and cross-sectional studies have suggested that cholesterol levels are higher in the fall and winter than in the spring and summer. Based on these findings, Tung and colleagues performed a post hoc analysis of the PROVE-IT study to determine if the variation in lipid levels exists in ACS patients.

In PROVE-IT, baseline LDL-cholesterol levels did not significantly differ by seasons, although baseline HDL-cholesterol levels were highest in the spring and summer. After four months of treatment, regardless of statin therapy, LDL-cholesterol levels were significantly lower and HDL-cholesterol levels significantly higher in the summer than the winter.

On-Treatment LDL- and HDL-Cholesterol Levels by Season in PROVE-IT

*p<0.001 for comparison between winter and summer

The researchers note that significantly more patients in both treatment arms reduced their LDL-cholesterol levels to less than 100 mg/dL in the summer than in the winter. Although the differences in LDL cholesterol in winter and summer are relatively small–a 6-mg/dL difference in the atorvastatin and pravastatin treatment arms–the seasonal difference, based on data from the Cholesterol Treatment Trialists’ Collaboration, suggests that this might be clinically significant, according to the authors.
At present, however, the PROVE-IT analysis should be considered exploratory, particularly since trial enrollment was not uniformly distributed over a single year, and because there was an unequal distribution of patients enrolled in different seasons. Also, there was limited data on diet, exercise, and other variables that might have affected the lipid results. Further studies, comment Tung and colleagues, are needed to determine if the diagnosis and treatment of hyperlipidemia based on the seasons would result in improved outcomes.

Tung P, Wiviott SD, Cannon CP, et al. Seasonal variation in lipids in patients following acute coronary syndrome on fixed doses of pravastatin (40 mg) or atorvastatin (80 mg) (from the Pravastatin or Atorvastatin Evaluation and Infection Therapy–Thrombolysis in Myocardial Infarction 22 [PROVE IT-TIMI 22] Study). Am J Cardiol 2009; 103:1056-1060.