[Influence of smoking on homocysteinemia at baseline and after methionine load]

Homocysteinemia (HC) and smoking are both important risk factors for vascular disease. In the present study, we intend to evaluate the influence of smoking habits on HC values as well as on vitamins B6, B12 and folic acid, co-factors of HC metabolism.

We measured fasting homocysteinemia (basal) and homocysteinemia 6 hours after an overload with 0.1 g methionine/kg body weight in 279 subjects. We also performed the dosage of plasma levels of B6 and B12 vitamins and of red cells folates. Smoking habits were inquired and the subjects were classified as non-smokers, current smokers or ex-smokers (if they had stopped smoking more than 1 month before the study). According to the smoking status, smokers were classified in three groups: less than 20 cigarettes a day, between 20 and 39 and 40 or more cigarettes a day. We studied basal and after methionine load homocysteinemia, B6, B12 and folic acid levels in each group.

Smokers presented significantly higher levels of basal and after methionine load homocysteinemia then non-smokers (10.6 +/- 4.9 vs 9.4 +/- 2.6, and 26.8 +/- 10.0 vs 24.3 +/- 7.4 mumol/L, respectively, p < 0.05 for both and B6 levels (29.2 +/- 12.0 versus 32.6 +/- 12.0 mumol/L, p < 0.05). B12 and folic levels were similar in the two groups. These results were quite similar either in the normal subjects or in the subjects with a history of a cardiovascular event. The subjects who smoked 40 or more cigarettes per day, compared with those who smoked less then 20 cigarettes per day, presented higher levels of basal homocysteinemia (12.4 +/- 2.9 vs 10.0 +/- 5.5 mumol/L, p < 0.05) and lower levels of B6 (24.7 +/- 8.1 vs 31.7 +/- 12.6 mumol/L, p < 0.05).

Smoking habits are related with the increase of basal and after methionine load homocysteinemia, probably because of a decrease in B6 vitamin levels. There is a proportional effect between the number of cigarettes smoked, B6 depletion and basal homocysteinemia increase. This study suggests that B6 vitamin supplements for smokers could decrease the vascular risk related with smoking habits.