Vitamin D is best known for helping the body build strong bones, but scientists are also studying its possible effects on the aging brain.
Research from Rutgers University suggests that the amount people take may matter, because a moderate dose was linked to better memory while a higher dose was linked to slower reaction speed.
The study was published in The Journals of Gerontology: Series A and was led by Rutgers researcher Sue Shapses. Researchers wanted to learn whether different daily amounts of vitamin D could affect thinking skills in older adults.
Vitamin D is produced in the skin when it is exposed to sunlight, and it is also found in some foods and supplements. Older adults are more likely to have low vitamin D levels because the skin becomes less efficient at making the vitamin with age, and some people spend less time outdoors.
Vitamin D may also play a role in the brain. Brain cells have receptors that respond to the vitamin, which has encouraged researchers to investigate whether vitamin D could influence memory, learning and other mental abilities.
The Rutgers study included overweight or obese women between 50 and 70 years old and lasted for one year. The participants were divided into groups that received 600, 2,000 or 4,000 international units, or IU, of vitamin D each day.
The 600-IU amount was close to the commonly recommended daily intake for adults in this age range. The other two groups received larger doses so researchers could see whether taking more vitamin D produced greater benefits.
The women also took part in a weight-loss program during the study. This was important because body weight and changes in weight can influence general health and may also affect how the body uses vitamin D.
After comparing the groups, researchers found an interesting pattern. Women taking 2,000 IU a day performed better on some tests of memory and learning than women taking 600 IU.
But taking more vitamin D did not appear to bring greater benefits. Women in the 2,000-IU group had somewhat slower reaction times, while those taking 4,000 IU showed an even greater slowing in their responses.
Reaction time describes how quickly a person responds to something they see or experience. This ability becomes particularly important with age because quick responses can help people correct their balance, avoid obstacles and react when they begin to slip or fall.
Falls are a major health concern for older adults because they can cause broken bones, loss of independence and other serious problems. Earlier research has raised concerns that high doses of vitamin D may increase the risk of falls in some older people, although scientists are still trying to understand why.
The Rutgers findings offer one possible clue by showing that higher vitamin D intake may affect reaction speed. However, the study did not prove that the slower reactions observed in the participants actually caused more falls or injuries.
There are also important limits to the research. The study focused on overweight and obese women aged 50 to 70, so the findings may not apply in the same way to men, younger adults, very old adults or people with different body weights.
More research is needed to determine which vitamin D levels are best for brain health and whether the ideal amount differs from person to person. Scientists also need to study how vitamin D interacts with other factors that influence the brain, including physical activity, sleep, blood pressure and diet.
The findings are a useful reminder that more of a nutrient is not always better. Vitamin D is essential for health, but people considering higher-dose supplements should discuss their individual needs with a health professional rather than assuming that a larger dose will provide greater benefits.
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