Zinc supplements increased vitamin A levels in older adults, according to a new study. Researchers recruited 387 men and women, aged 55 to 85, who took a placebo, 15 mg of zinc—which is the U.S. Recommended Dietary Allowance—or 30 mg of zinc per day, for six months. Researchers measured blood-plasma levels of vitamin A (retinol) at the start of the study, and at three and six months, and found that levels of vitamin A increased as the zinc dosage and length of treatment time increased. In explaining the reason for the study, researchers noted that low zinc levels can prevent the body from absorbing vitamin A.