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The determinants of plasma beta-carotene: interaction between smoking and other lifestyle factors.

OBJECTIVE
To assess the effect of cigarette smoking on the relationship between dietary intake and circulating levels of beta-carotene.


DESIGN
A secondary analysis of data collected for the Diet and Nutritional Survey of British Adults by The Department of Health and The Ministry of Agriculture, Fisheries and Food; the study was a cross-sectional survey of a representative sample of the British population.


SETTING
The study was conducted on a free living adult (16-64 years of age) population resident in Great Britain.


SUBJECTS
1483 subjects completed a seven day weighed inventory and provided a blood sample.


RESULTS
Smokers had statistically significantly lower dietary intakes and circulating levels of beta-carotene than non-smokers. At the same level of dietary intake, smokers were more likely to have lower circulating levels than non-smokers. For every 1000 micrograms change in dietary intake, there was a 0.01 mumol/l change in plasma beta-carotene in smokers and a 0.04 mumol/l change in non-smokers. The effect of smoking on circulating levels of beta-carotene persisted after adjusting for other factors.


CONCLUSIONS
The results suggest that smoking places extra demands on the host; the higher risk of heart disease for smokers may be due to a combination of an increased inflammatory response, reduced host defences, and increased levels of circulating LDL. Failure to take account of the interaction between risk factors may distort the estimates of the relative importance of each factor when considered in isolation.