Investigators found that children whose parents exposed them to secondhand smoke at home had lower blood concentrations of the vitamin compared with children of non-smokers.

The findings echo those of studies showing that active smoking may deplete a person's vitamin C stores. And they support the idea that people exposed to secondhand smoke may have a particularly important need for dietary vitamin C, according to the study authors.

They recommend that children exposed to secondhand smoke "be urged to eat more vitamin C-rich foods" or take supplements. Parents and expectant parents should, of course, attempt to quit smoking.

Good food sources of vitamin C include citrus fruits, strawberries, broccoli and potatoes. Many other fruits and vegetables contain smaller amounts of the nutrient.

Vitamin C is needed for normal growth and development and acts as a powerful antioxidant. That means it helps neutralize cell-damaging substances in the body called free radicals. Smoking, on the other hand, promotes free-radical damage, which is thought to contribute to aging and chronic disease.

Although a number of studies have suggested that smokers themselves may be low on vitamin C, little has been known about the vitamin status of the people who live with smokers, according to the authors of the new study.

To investigate, Dr. Alan M. Preston and colleagues at the University of Puerto Rico in San Juan measured vitamin C levels and secondhand smoke exposure among 512 children ages 2 to 12.

They found that the average blood level of vitamin C was lower in the half whose parents smoked at home--despite a dietary intake of vitamin C that was similar to that of the other children. Further analysis showed that the association was confined to girls, for reasons that are unclear, according to the researchers.

They report the findings in the January issue of the American Journal of Clinical Nutrition (news - web sites).

Using urine samples to test for a biological marker of smoke exposure, the researchers also found that even "very low exposure" to secondhand smoke was associated with lower levels of vitamin C.

"It is rather remarkable," they note, "that this reduction in blood (vitamin C) occurs at such a minimal amount of smoke exposure."

SOURCE: American Journal of Clinical Nutrition 2003;77:167-172.