A Cochrane meta-analysis has found no evidence that any
vitamin or mineral supplementation strategy for cognitively healthy adults in
mid or late life has a meaningful effect on cognitive decline or dementia,
although the evidence does not permit definitive conclusions.

The meta-analysis published in the Cochrane Database of
Systematic Reviews included 28 studies with more than 83 000 participants. This
review aimed to find out whether people aged 40 years or older could maintain
their mental abilities or reduce their risk of dementia by taking vitamin or
mineral supplements. The 28 included trials were grouped according to the kind
of supplement they used and how it might work.

According to the researchers, most of the trials were not
originally designed to study cognition or dementia and used only simple
measures of cognition. Very few studies investigated whether participants
developed dementia.

There were 14 trials of B vitamins (folic acid, vitamin B6,
vitamin B12) with nearly 28 000 participants, mainly in their 60s and 70s. Most
of these trials were quite short (less than two years). No evidence was found that
B vitamins had any effect on cognition.

There were 8 trials of antioxidant vitamins (beta‐carotene/vitamin
A, vitamin C, vitamin E) with approximately 47 000 participants. These trials
tended to be longer than the B vitamin trials so may have had more chance of
detecting effects on dementia and cognitive decline. The results were mixed. Low‐certainty
evidence was found of better overall cognitive function after an average of 18
years taking beta‐carotene and after five years to 10 years taking vitamin C,
but no effects after shorter periods of treatment. There were also small
benefits of beta‐carotene, vitamin C, and antioxidant combinations on memory at
some time points but not others. There was no evidence of any benefits from
vitamin E alone. Two studies examined the risk of developing dementia. One
found no effect of a combination of antioxidant vitamins and the other found no
effect of vitamin E, either alone or combined with the mineral selenium. Most
of the studies did not report any information about harmful effects.

There was a small trial of vitamin D supplements which found
they probably had no effect on cognition over six months. There were longer
trials of vitamin D with calcium (one trial), zinc and copper (one trial), and
complex multivitamins (three trials). All lasted between five and 10 years, but
none of them found any evidence of beneficial effects on cognition. One trial
found no effect of selenium taken for approximately five years on the risk of
developing dementia.

“We found no good evidence to suggest that middle‐aged or
older people can preserve cognitive function or prevent dementia by taking
vitamin or mineral supplements. There were a few positive results associated
with long‐term use of antioxidant vitamins, particularly beta‐carotene and
vitamin C, although the effects were small. Further research into the effects
of these vitamins may be worthwhile,” the researchers concluded.


Reference: Vitamin
and mineral supplementation for maintaining cognitive function in cognitively
healthy people in mid and late life. Cochrane Systematic Review – Intervention Version
published: 17 December 2018. https://www.cochranelibrary.com/cdsr/doi/10.1002/14651858.CD011906.pub2/full