Seasonal variation of serum lipids in an elderly population.

Introduction

Seasonal variation of plasma lipids has been shown in a large longitudinal trial of 35-59-year-old men [1]. Peak levels of total cholesterol, low-density lipoprotein (LDL) cholesterol and high-density lipoprotein (HDL) cholesterol all occurred in winter. This confirmed the results of earlier studies which had generally shown highest levels of total cholesterol in winter [2-4], although some found peaks in spring [5] and autumn [6], and some found no seasonal variation of total cholesterol [7, 8]. Seasonal variation in triglycerides seems to be less consistent but peak levels may occur in the autumn [1]. Most of the subjects in these studies were middle-aged adults and little is known of seasonal variation of serum lipids in elderly people. Since cardiovascular mortality is greatest in the old [9], any seasonal variation in associated risk factors could be of greater importance to this age group.

We investigated seasonal variation of the major known cardiovascular disease risk factors in a cohort of people aged 64-74 years and our findings with regard to serum lipids are presented in this paper.

Methods

One hundred volunteers from a single general practice in Cambridge entered the study after postal invitation. Selection for mailing was random and response rate was 45%. Two subjects withdrew consent and two died early in the study, making their results unsuitable for seasonal analysis. The results from the remaining 96 subjects are reported here.

Subjects were visited in their own homes at 2-monthly intervals from January 1991 to February 1992. The dates encompassing the visits are given in Table I. On each of the seven visits blood was withdrawn from an antecubital vein with the subject seated and without venostasis. The subjects were not fasting but all visits to each individual were planned to occur at the same time of day and on the same day of the week (Monday to Friday). This was achieved in 94% of cases.

 
Table I. Dates of study visits 
Visit              1991 
1     7 January-8 February 
2     4 March-5 April 
3     6 May-7 June 
4     8 July-9 August 
5     2 September-4 October 
6     4 November-6 December 
              1992 
7     6 January-7 February 

Serum total cholesterol, HDL cholesterol and triglycerides were measured by standard laboratory techniques on the RA1000 …