SEASONAL-VARIATION IN PARAMETERS RELATED TO CORONARY HEART-DISEASE RISK IN YOUNG MEN

Seasonal variation in the plasma lipids and lipoproteins is reported i n the literature. Whether this variation is the result of changes in d iet or other factors has not been adequately addressed. We investigate d the effects of a controlled diet on the seasonal variation in the le vels of plasma lipids and apolipoproteins and also on the excretion of urine metabolites of TXA(2) and PGI(2) in healthy males. Two well-con trolled diet studies were conducted to evaluate effects of dietary fat ty acids on plasma lipids (Studies 1 and 2; n = 33) and eicosanoid exc retion (Study 2 only; n = 15). Participants consumed whole-food test d iets in a randomized, four-period crossover design during each 26-day experimental period. A non-intervention control group also participate d in each study (Study 1, n = 12; Study 2, n = 11). Blood was collecte d monthly and analyzed for plasma lipids and apolipoproteins A-1 (Apo A-1) and B100 (Apo B). Twenty-four hour urine samples were collected m onthly only in Study 2 and analyzed for TXB(2) and 6-keto-PGF(1 alpha) by RIA. Seasonal fluctuations were observed in all subjects in plasma Apo A-1 (zenith = July, with 95% CI June-July; P < 0.05) and Apo B (z enith = October, 95% CI September-November, P < 0.05). Although there was no significant variation in plasma cholesterol levels, the increas e in Apo B is consistent with an increase in LDL particle number durin g the fall/winter. Additionally, excretion of both eicosanoid metaboli tes and the ratio of 6-keto-PGF(1 alpha)/TXB(2) was markedly elevated in July (95% CI June-July, P < 0.001). These seasonal fluctuations wer e observed both in participants who consumed a highly-controlled exper imental diet and in the non-intervention controls. Thus, these results suggest a diet-independent seasonal variation in parameters thought t o be involved in coronary heart disease risk status. An understanding of these variations is important not only for clinical evaluation and metabolic study design issues, but more importantly, to clarify their clinical significance with the seasonal incidence of CHD events.