Public Release: 

As Vitamin B-6 levels go down, numbers of DNA strand breaks go up

Suggests taking another look at Vitamin B-6 recommended RDA

Federation of American Societies for Experimental Biology

Taking baseline data on the first day of a Washington State University study, researchers found that four of six young, healthy moderate smokers -- men and women who smoked less than a pack a day -- had unacceptably low blood levels of Vitamin B-6, a vitamin believed to be protective against the DNA damage that can lead to cancers. Only one of the otherwise comparable non-smokers had unacceptable Vitamin B-6 status. After three months of consuming increasingly high levels of dietary and/or supplemental Vitamin B-6, the smokers eventually reached acceptable levels. But they never caught up with their non-smoking counterparts. Considering Vitamin B-6's role in DNA synthesis and repair, these results further convinced the researchers that the current RDA for this critical vitamin is too low for even moderate smokers and could be too low for the population as a whole.

Dr. Terry Shultz presented the study at the Experimental Biology 2003 meeting in San Diego, as part of the American Society for Nutritional Sciences program.

In several large population studies, people with a higher intake of Vitamin B-6 were found to have a lower risk of colon, prostate, lung, gastric and pancreatic cancers. The good news from this study, says Dr. Shultz, is that adding Vitamin B-6 to the diet rapidly improved both smokers' and non-smokers' Vitamin B-6 status and, equally rapidly, decreased the number of DNA strand breaks in both groups.

That makes sense biochemically, he says. The body uses Vitamin B-6 to convert the vitamin folate to a form that can produce thymine, a component of DNA. If the body doesn't have enough Vitamin B-6, it doesn't make enough thymine and it tries to make do by substituting uracil. Uracil is not a normal component of DNA, and the normal DNA repair mechanisms of the cell become stressed. This inefficiency in the normal repair mechanisms leads to breaks in DNA strands and instability of chromosomes -- possible first steps in the development of cancerous cells.

The study had four phases.

In the first 28 days, after baseline measures of Vitamin B-6 status and DNA strand breaks, six smokers and six non-smokers were given carefully controlled diets containing only marginal amounts of Vitamin B-6. Because the diet was designed to be low in Vitamin B-6, foods high in Vitamin B-6 like cereals, beef, chicken, fish, legumes, soy products and bananas, were limited. The diet was composed of other commonly consumed foods and was adequate in all other nutrients. At the end of this depletion period, the researchers found that all subjects had lower Vitamin B-6 levels and higher numbers of DNA strand breaks. The smokers' already low Vitamin B-6 levels had fallen lower, of course, but the two groups appeared similar in the number of DNA strand breaks, possibly because the researchers only measured the total lymphocyte profile rather than looking at subsets, which may have been affected differently.

During the second month, the subjects ate only a carefully controlled diet that included 1.4 mg of Vitamin B-6 (dietary plus some supplementation), approximately the RDA.

During the third month, subjects continued to eat only what the researchers gave them but Vitamin B-6 intake was raised to 2.2 mg per day.

And during the fourth and final month, subjects were allowed to eat whatever they wanted, but they were supplemented with 10.3 mg of Vitamin B-6 per day, more than seven times the recommended RDA.

As the amount of Vitamin B-6 in the diet went up, body levels of Vitamin B-6 went up and DNA strand breaks went down, beginning as early as the first month of Vitamin B-6 supplementation.

Dr. Shultz says that Vitamin B-6 has been identified as a nutrient with a high prevalence of inadequate dietary intake in the general population. This study suggests smokers are even more likely at risk for low Vitamin B-6 and thus for the problems it presents.

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(American Society for Nutritional Sciences)

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