Within-subjects seasonal variation and determinants of inter-individual variations of plasma beta-carotene.

We studied determinants of plasma beta-carotene in a sample of 98 normal volunteers. Blood samples were collected and 4-day weighed dietary records kept for each season of the year. Information on tobacco use and demographic and socio-economic data was elicited at the first interview. There was a peak of plasma beta-carotene in the fall, whereas the dietary beta-carotene peak occurred in summer. In a regression analysis involving a variety of independent variables, the only statistically significant determinants of plasma beta-carotene for non-smokers were dietary beta-carotene, sex, serum cholesterol and triglycerides. The number of cigarettes/day was introduced into the model for smokers and a significant negative coefficient was obtained for this variable. Interaction between dietary beta-carotene and tobacco use was shown to be a significant determinant of plasma beta-carotene for the total sample.