B6 -Don't Belittle this Vitamin
As vitamins go, B6 doesn't fly high on the radar screen of
most consumers. However, owing to its many benefits—which include protecting DNA—this unsung nutritional hero
shouldn't be neglected, argue a pair of scientists. Last week, they reported data showing that when people consume
diets low in this vitamin, their blood has higher rates of DNA-strand breakage than when those same test volunteers
get ample amounts of B6.
Cigarette smoking appears to rob the
body of much of its vitamin B6, a nutrient important to protecting DNA.
"The good news is that following . . . diets containing ample amounts
of the vitamin, the number of DNA-strand breaks fell back to normal," according to study coauthor Terry D. Shultz
of Washington State University. This was true even in smokers, who typically have low blood concentrations of
vitamin B6. However, the nutritional biochemist points out that smokers who took part in this experiment
lit up only an average of 16 cigarettes a day—less than a pack.
Why care about DNA-strand breaks? Because they're "one thing that can
lead to cancer," notes Christine M. Hansen, now at Iowa State University, also a coauthor of the new study reported
last week in San Diego at Experimental Biology 2003.
Indeed, support for the idea that B6 may have anticancer
benefits also appears in a paper earlier this year in the Journal of the National Cancer Institute. In
that study, researchers led by a team at the Harvard School of Public Health reported that among nearly 33,000
women, those with the highest blood concentrations of vitamin B6 face a 30 percent lower risk of breast
cancer than do women with the lowest concentrations of the vitamin in their blood. The comparison was between the
top fifth of study volunteers versus the bottom fifth, according to their B6 blood
The way for DNA to B healthy
Vitamin B6 comes in six forms. All are coenzymes—partners
for about 100 true enzymes that help build or break down various biologically active chemicals.
The rungs of DNA's ladderlike structure are made of paired
combinations of four chemicals, one of which is thymine. Vitamin B6 prods a reaction in the body that
converts folate—another B vitamin—into thymine. So, when B6 concentrations are low, the availability of
thymine also drops. DNA sometimes responds, Shultz notes, by inappropriately substituting uracil, a related
chemical, in some of the rungs.
The body has various enzymes to cull heavily damaged DNA and others to
repair what can be fixed. Ordinarily, when uracil gets into DNA, repair enzymes swoop in, snip it out, and insert a
thymine. However, if too many uracil mistakes occur, "the repair-enzyme mechanisms can become overwhelmed," Shultz
told Science News Online. The result: A strand of DNA may get cut open at the uracil site but not stitched
back together with its missing thymine.
In the new study . . .
To evaluate the special vulnerability of smokers, the Washington State
team recruited 12 men and women, half of them smokers, for a feeding experiment. All volunteers initially exhibited
about the same, low background concentration of DNA-strand breaks in a type of white blood cell, although the
smokers had roughly 50 percent lower starting B6 blood concentrations, observes Shultz.
Over the next 5 months, the researchers provided all meals for these
volunteers, ages 21 to 44. Month to month, the only nutritional change to their diet was the quantity of vitamin
For the first month, the men and women received a diet low in
B6. The recommended dietary allowance (RDA) for adults is 1.3 milligrams per day, but the researchers
fed the study participants only 0.7 mg/day during this starting period.
By the end of the month, the volunteers had about 75 percent more
DNA-strand breaks in their white blood cells than when they started.
The researchers then upped the recruits' B6 intake to the
RDA for 1 month—and counts of DNA breaks fell back to normal. In subsequent months, the scientists increased the
B6 supplementation even more—eventually to 10 mg/day. Though the recruits' DNA-break counts continued to
fall, they never went far below their values at the beginning of the study.
The researchers are a bit perplexed why they didn't see a bigger
difference between smokers and nonsmokers, "but perhaps that's because we didn't look at subsets of [white blood
cells]," says Shultz. Some classes of cells might have been more vulnerable to DNA-strand breaks than others, he
"The take-home message here is that there could be a high prevalence
of inadequate vitamin B6 intake in the general population," Shultz says. Indeed, the Institute of
Medicine has found that much of the U.S. population doesn't even consume the estimated average requirement, which
at 1.1 mg/day is below the RDA. Some 10 to 25 percent of men over 50 don't get 1.1 mg/day, and women do even worse.
A quarter to a half of women over 50 and pregnant women of any age fail to consume the estimated average
requirement of vitamin B6.
People who think they may be low in vitamin B6—and this
probably should include all smokers—may want to increase their intake of foods rich in the nutrient, especially
fortified cereals, bananas, avocados, beef, poultry, fish, and legumes.
2003. As vitamin B-6 levels go down, numbers of DNA
strand breaks go up. Federation of American Societies for Experimental Biology press release. April 14. Available
Shultz, T.D., C.M. Hansen, et al. 2003.
Lymphocyte DNA strand breaks in smokers and nonsmokers are related to vitamin B-6 intake and metabolite
concentrations in plasma and urine. Experimental Biology 2003. April 14. San Diego. Abstract available at
Standing Committee on the Scientific Evaluation of
Dietary Reference Intakes and its Panel on Folate, Other B Vitamins, and Choline and Subcommittee on Upper
Reference Levels of Nutrients, Food and Nutrition Board, Institute of Medicine. 1998. Dietary Reference Intakes
for Thiamin, Riboflavin, Niacin, Vitamin B6, Folate, Vitamin B12, Pantothenic Acid, Biotin,
and Choline. Washington, D.C.: National Academy Press. Available at http://www.nap.edu/catalog/6015.html.
Zhang, S.M., et al. 2003. Plasma folate,
vitamin B6, vitamin B12, homocysteine, and risk of breast cancer. Journal of the National
Cancer Institute 95(March 5):373-380. Abstract available at http://jncicancerspectrum.oupjournals.org/cgi/content/abstract/jnci;95/5/373.
2003. The vitamin that does almost everything.
UC Berkeley Wellness Letter 19(April):1. Available at http://www.wellnessletter.com/html/wl/wlFeatured0403.html#top.
Hansen, C.M., T.D. Shultz, et al. Vitamin
B-6 intake and smoking status influence lymphocyte serine hydroxymethyltransferase activity in healthy adults.
Experimental Biology 2003. April 11-15. San Diego. Abstract available at http://www.biosis-select.org/faseb/data/FASEB002081.html.
Harder, B. 2002. Vitamin void: Heart disease may
lurk in B12 deficiency. Science News 161(Feb. 16):100. Available to subscribers at http://www.sciencenews.org/20020216/fob4.asp.
Raloff, J. 1998. B vitamins bestow heartfelt
benefits. Science News 153(Feb. 14):105.
Seppa, N. 2002. High homocysteine tied to
Alzheimer's. Science News 161(March 2):141. Available to subscribers at http://www.sciencenews.org/20020302/note11.asp.
_____. 2000. A hint at a healthful effect of beer.
Science News 157(May 13):317. Available to subscribers at http://www.sciencenews.org/20000513/note18.asp.