by Craig Weatherby
Lab studies have suggested that higher vitamin D blood levels may boost cognitive functions of the brain.
And people with impaired cognitive function are more likely to develop dementia, with some small clinical studies suggesting that low levels of vitamin D may be associated with dementia and poor cognitive function.
Last month, we reported on a large population study that added evidence linking higher vitamin D blood levels to better brain health (See “Vitamin D May Boost Aging Brains.”)
|Fish fit the vitamin D bill; Sockeye salmon stand out|
In addition to getting vitamin D from supplements, certain fish rank among the very few substantial food sources of vitamin D, far outranking milk and other D-fortified foods.
Among fish, wild Sockeye Salmon may be the richest source of all, with a single 3.5 ounce serving surpassing the US RDA of 400 IU by about 70 percent:
Vitamin D per 3.5 ounce serving*
Sockeye Salmon 687 IU
Albacore Tuna 544 IU
Silver Salmon 430 IU
King Salmon 236 IU
Sardines 222 IU
Sablefish 169 IU
Halibut 162 IU
*For our full test results, click here.
It found that people with optimum levels of vitamin D were much less likely to be cognitively impaired.
In other words, having too little vitamin D in your body appeared to make it harder to think… a status associated with greater risk of developing Alzheimer’s disease (AD) and other forms of dementia.
Now, a new study of similar design has produced similar results in favor of viewing this hormone-like vitamin as a necessary brain “nutrient”.
A joint British-American team reports finding that people with the lowest vitamin D levels were more than twice as likely to have impaired understanding, compared to those with the highest vitamin D levels (Llewellyn DJ et al. 2009).
Low vitamin D levels linked to higher risk of dementia
The results of the new population study—by researchers from the UK's Peninsula Medical School and University of Cambridge, as well as the University of Michigan— again link a lack of vitamin D to cognitive impairment in older people.
The study is the first of its scale to identify this relationship, and prompted researchers to suggest vitamin D supplementation as a possible way to reduce the risk of dementia.
The researchers recruited 1,766 adults over the age of 65—708 men and 1,058 women—who were participating in the Health Survey for England.
Their levels of cognitive function were assessed using a common screening test called the Abbreviated Mental Test (AMT).
Fasting blood samples were also taken, and their levels of vitamin D were measured.
The scientists then examined the relationship between blood vitamin D levels and cognitive impairment, adjusting for other factors known to affect AMT cognition scores.
Their analysis showed that those with the lowest blood vitamin D levels—that is, 8 to 30 nmol/L (nanomoles per liter)— were twice as likely to be cognitively impaired, compared to those with the highest blood levels (66 to 170 nmol/L).
And they found that the relationship between vitamin D levels and cognitive function was most pronounced at vitamin D levels below 35 nmol/L.
By way of comparison, most vitamin D experts recommend reaching minimum blood levels ranging from 90 to 120 nmol/L—the equivalent of 36 to 48 ng/mL (nanograms per liter)—to enable optimal health.
The high end of the normal range of human vitamin D blood levels extends beyond the proven safe level of 200 nmol/L (80 ng/mL).
The non-clinical, uncontrolled design of this study means they could not determine whether low levels of vitamin D actually cause or promote cognitive impairment.
However, they did say that their findings add to accumulating data that supports, as they put it, “…previously unsuspected roles for vitamin D in brain development and neuro-protection.”
And they concluded, “Further research is warranted to investigate whether vitamin D supplementation is a cost effective and safe way of reducing the incidence of cognitive impairment in the growing elderly population around the world.”
Every passing week seems to bring new evidence that people with high levels of the “sunshine-and-seafood” vitamin enjoy a wide range of health benefits and protections.
- Llewellyn DJ, Langa K, Lang I. Serum 25-Hydroxyvitamin D Concentration and Cognitive Impairment. J Geriatr Psychiatry Neurol. 2009 Feb 4. [Epub ahead of print]
- Lee DM et al.; EMAS study group. Association between 25-hydroxyvitamin D levels and cognitive performance in middle-aged and older European men. J Neurol Neurosurg Psychiatry. 2009 Jul;80(7):722-9. Epub 2009 May 21.