Everybody knows that vitamin D is good for healthy bones. That is why they fortify milk with it. You may not know it is good for certain skin conditions, such is the one I have that appears every Winter when I don’t get enough sunlight, even though I live in Texas. Taking 2,000 IU vitamin D3 daily has stopped this problem. I read also that vitamin D stimulates the immune system. I am now surprised to learn it might be helpful for memory.
A research group in the United Kingdom, recognizing that many people are vitamin D deficient there because they don’t get much sunlight to help the skin generate vitamin D, pursued the question of why there are molecular receptors for vitamin D in the brain. What is that all about?
Some previous studies by other groups had shown vitamin D has protective effects on the brain and enhances its activity. Other studies had shown that low serum levels of the 25 (OH) form of vitamin D were associated with poor cognitive test performance among patients with mild Alzheimer disease, and a study of older adults revealed a positive correlation between 25(OH) D blood levels and scores on a mental function test.
This British study looked at a large population (3,133) of middle-aged and older men to evaluate the association between vitamin D levels and cognition. Specifically, the investigators tested blood levels of serum 25-hydroxyvitamin D in non-institutionalized European men, aged 40–79 years, and compared those levels with performance on three mental-function tests, one of which was a specific test of memory. High blood levels of vitamin D were associated with better performance on a test for analyzing complex visual images and a recognition memory test.
Studies like this are exceedingly complex, because there are many hard-to-control variables (the paper had more than 21 authors). Not surprisingly, depression, physical activity, physical performance, and smoking were all consistently associated with both cognitive test scores and 25(OH) D concentrations. Some mental-test scores, together with 25(OH)D levels, were additionally associated with drinking one or more alcoholic drink per week. Also, as expected, 25(OH) D levels varied markedly by season, peaking in the summer and reaching bottom in the winter.
After additional adjustments for age, education level, depression, basal metabolism, physical activity, physical performance, smoking, alcohol consumption, season, higher 25(OH) D concentrations were found to be associated more specifically with psychomotor speed and visual scanning.
Vitamin D exists in two common forms; vitamin D2 and D3. The form mainly produced in the skin and derived from natural dietary sources is vitamin D3, whereas the primary source of vitamin D2 is multivitamin preparations and some fortified foods. There have been conflicting reports as to whether vitamin D2 and vitamin D3 are equally effective at maintaining 25(OH) D levels,
Nobody knows why vitamin D affects brain function, but the existence of specific molecular receptors inside the nucleus of neurons cannot be dismissed. Possibilities include direct effects on promoting synthesis of the alertness-producing neurotransmitter, acetylcholine, or more indirect effects on intracellular calcium (calcium is a signaling molecule in nerve cells). Other possible ways vitamin D might help brain function include its ability to stimulate synthesis of nerve growth factor. Vitamin D is neuroprotective against stroke and, by its ability to attenuate neurotoxic insults, could have a major impact in preventing neurodegenerative diseases. Vitamin D has the potential to increase glutathione which helps with detoxification and protection against free radical stress.
It is still an open question whether vitamin D helps memory. But I will keep taking my vitamin D3 to help my skin condition. Any benefit to my memory will be a much-appreciated bonus.
Lee, David M. et al. 2009. Association between 25-hydroxyvitamin D levels and cognitive performance in middle-aged and older European men. J. Neurol. Neurosurg. Psychiatry. 80:22-729. Doi: 10.1136/jnnp.2008.165720.