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Information on the latest vitamin D news and research.

Find out more information on deficiency, supplementation, sun exposure, and how vitamin D relates to your health.

Cognitive impairment

Cognitive dysfunction (or brain fog) is defined as unusually poor mental function. This causes confusion, forgetfulness, and difficulty concentrating.

Risk factors

Risk factors for cognitive impairment include:

  • Old age
  • Smoking
  • Lack of exercise
  • Diet high in animal fats
  • Diet low in vegetables and fish
  • Obesity

Unhealthy diets also increase the risk of cardiovascular disease, hypertension, and diabetes.

Diets high in fat and protein make the digestive tract more acidic. These diets increase the absorption of heavy metals and aluminum. These toxins may generate free radicals in the brain. Free radicals destroy neurons and impair brain function.

Sunlight exposure and cognitive impairment risk

There are no reported studies linking solar radiation to brain function. However, ultraviolet-B (UVB) light is the primary source of vitamin D for most people. Studies have confirmed the positive effects of vitamin D and brain function.

Vitamin D and cognitive impairment

Vitamin D levels

Lower vitamin D blood levels are linked to a higher risk of cognitive impairment. This has been confirmed in many studies:

  • African-Americans and European Americans with low vitamin D blood levels performed much worse on a cognitive performance test and slightly worse on a physical performance test.
  • European men with lower vitamin D levels performed worse on a test with numbers
  • Elderly blacks and non-blacks with higher vitamin D levels did better on decision making and attention/ processing speed tests. However, they did not perform better on memory tests.
  • British adults aged 65 years and older with vitamin D levels less than 12 ng/mL (30 nmol/L) were 2.3 times as likely to have cognitive impairment as those with vitamin D levels above 26 ng/mL (66 nmol/L).
  • Older Italian adults with vitamin D levels below 10 ng/mL (25 nmol/L) had a 60% increased risk of decline in global cognitive function compared to those with vitamin D levels above 20 ng/mL (50 nmol/L). There was also a 30% increased risk of decline in decision making.
  • Adults greater than 65 years of age with  vitamin D levels below 10 ng/mL (25 nmol/L) had 4 times the increased risk of cognitive impairment compared to those with levels above 30 ng/mL (75 nmol/L).

How vitamin D works

Vitamin D may protect the brain in the following ways:

  • Reduce the risk of diseases that affect the brain (cardiovascular disease and hypertension)
  • Provide antioxidative mechanisms
  • Regulate calcium levels
  • Regulate the immune system
  • Enhance nerve conduction (signals)
  • Helps rid body of toxins


Vitamin D levels above 40 ng/mL (100 nmol/L) may reduce the risk of cognitive impairment. To achieve these levels, most people need to take 1000–5000 international units/day of vitamin D3 (cholecalciferol). But there is considerable variation from person to person. The vitamin D blood level should be measured before taking vitamin D supplements or increasing solar UVB exposure. Vitamin D levels should also be measured a few months later.


There are no reported studies on treating cognitive impairment with vitamin D. However, several trials are being organized around the world.


This evidence summary was written by:

William B. Grant, Ph.D.
Sunlight, Nutrition, and Health Research Center (SUNARC)
P.O. Box 641603
San Francisco, CA 94164-1603, USA

The summary was reviewed by:

  • Cedric Annweiler <ceannweiler@chu-angers.fr>

Complete bibliography of research used in this summary

The research we have cited in our summary is listed below, with links to PubMed abstracts and full-text for those who wish to explore further.


  1. Annweiler, C. Allali, G. Allain, P. Bridenbaugh, S. Schott, A. M. Kressig, R. W. Beauchet, O. Vitamin D and cognitive performance in adults: a systematic review. Eur J Neurol. 2009 Oct; 16 (10): 1083-9.
  2. Annweiler, C. Schott, A. M. Allali, G. Bridenbaugh, S. A. Kressig, R. W. Allain, P. Herrmann, F. R. Beauchet, O. Association of vitamin D deficiency with cognitive impairment in older women: cross-sectional study. Neurology. 2010 Jan 5; 74 (1): 27-32.
  3. Annweiler, C. Schott, A. M. Rolland, Y. Blain, H. Herrmann, F. R. Beauchet, O. Dietary intakes of vitamin D and cognition in older women: A large population-based study. Neurology, in press.
  4. Buell, J. S. Dawson-Hughes, B. Vitamin D and neurocognitive dysfunction: preventing “D”ecline?. Mol Aspects Med. 2008 Dec; 29 (6): 415-22.
  5. Buell, J. S. Dawson-Hughes, B. Scott, T. M. Weiner, D. E. Dallal, G. E. Qui, W. Q. Bergethon, P. Rosenberg, I. H. Folstein, M. F. Patz, S. Bhadelia, R. A. Tucker, K. L. 25-Hydroxyvitamin D, dementia, and cerebrovascular pathology in elders receiving home services. Neurology. Jan 5; 74 (1): 18-26.
  6. Buell, J. S. Scott, T. M. Dawson-Hughes, B. Dallal, G. E. Rosenberg, I. H. Folstein, M. F. Tucker, K. L. Vitamin D is associated with cognitive function in elders receiving home health services. J Gerontol A Biol Sci Med Sci. 2009 Aug; 64 (8): 888-95.
  7. Johnson, K. C. Margolis, K. L. Espeland, M. A. Colenda, C. C. Fillit, H. Manson, J. E. Masaki, K. H. Mouton, C. P. Prineas, R. Robinson, J. G. Wassertheil-Smoller, S. A prospective study of the effect of hypertension and baseline blood pressure on cognitive decline and dementia in postmenopausal women: the Women’s Health Initiative Memory Study. J Am Geriatr Soc. 2008 Aug; 56 (8): 1449-58.
  8. Jorde, R. Waterloo, K. Saleh, F. Haug, E. Svartberg, J. Neuropsychological function in relation to serum parathyroid hormone and serum 25-hydroxyvitamin D levels. The Tromso study. J Neurol. 2006 Apr; 253 (4): 464-70.
  9. Lee, D. M. Tajar, A. Ulubaev, A. Pendleton, N. O’Neill, T. W. O’Connor, D. B. Bartfai, G. Boonen, S. Bouillon, R. Casanueva, F. F. Finn, J. D. Forti, G. Giwercman, A. Han, T. S. Huhtaniemi, I. T. Kula, K. Lean, M. E. Punab, M. Silman, A. J. Vanderschueren, D. Wu, F. C. 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.
  10. Llewellyn, D. J. Lang, I. A. Langa, K. M. Muniz-Terrera, G. Phillips, C. L. Cherubini, A. Ferrucci, L. Melzer, D. Vitamin D and risk of cognitive decline in elderly persons. Arch Intern Med. Jul 12; 170 (13): 1135-41.
  11. Llewellyn, D. J. Langa, K. M. Lang, I. A. Serum 25-hydroxyvitamin D concentration and cognitive impairment. J Geriatr Psychiatry Neurol. 2009 Sep; 22 (3): 188-95.
  12. MacLaughlin, J. Holick, M. F. Aging decreases the capacity of human skin to produce vitamin D3. J Clin Invest. 1985 Oct; 76 (4): 1536-8.
  13. McCann, J. C. Ames, B. N. Is there convincing biological or behavioral evidence linking vitamin D deficiency to brain dysfunction?. FASEB J. 2008 Apr; 22 (4): 982-1001.
  14. McGrath, J. Scragg, R. Chant, D. Eyles, D. Burne, T. Obradovic, D. No association between serum 25-hydroxyvitamin D3 level and performance on psychometric tests in NHANES III. Neuroepidemiology. 2007; 29 (1-2): 49-54.
  15. Miller, J. W. Vitamin D and cognitive function in older adults: are we concerned about vitamin D-mentia?. Neurology. Jan 5; 74 (1): 13-5.
  16. Minasyan, A. Keisala, T. Lou, Y. R. Kalueff, A. V. Tuohimaa, P. Neophobia, sensory and cognitive functions, and hedonic responses in vitamin D receptor mutant mice. J Steroid Biochem Mol Biol. 2007 May; 104 (3-5): 274-80.
  17. Oudshoorn, C. Mattace-Raso, F. U. van der Velde, N. Colin, E. M. van der Cammen, T. J. Higher serum vitamin D3 levels are associated with better cognitive test performance in patients with Alzheimer’s disease. Dement Geriatr Cogn Disord. 2008; 25 (6): 539-43.
  18. Parker, J. Hashmi, O. Dutton, D. Mavrodaris, A. Stranges, S. Kandala, N. B. Clarke, A. Franco, O. H. Levels of vitamin D and cardiometabolic disorders: systematic review and meta-analysis. Maturitas. Mar; 65 (3): 225-36.
  19. Petersen, R. C. Smith, G. E. Waring, S. C. Ivnik, R. J. Tangalos, E. G. Kokmen, E. Mild cognitive impairment: clinical characterization and outcome. Arch Neurol. 1999 Mar; 56 (3): 303-8.
  20. Przybelski, R. J. Binkley, N. C. Is vitamin D important for preserving cognition? A positive correlation of serum 25-hydroxyvitamin D concentration with cognitive function. Arch Biochem Biophys. 2007 Apr 15; 460 (2): 202-5.
  21. Seamans, K. M. Hill, T. R. Scully, L. Meunier, N. Andrillo-Sanchez, M. Polito, A. Hininger-Favier, I. Ciarapica, D. Simpson, E. E. Stewart-Knox, B. J. O’Connor, J. M. Coudray, C. Cashman, K. D. Vitamin D status and measures of cognitive function in healthy older European adults. Eur J Clin Nutr. Aug 11;
  22. Slinin, Y. Paudel, M. L. Taylor, B. C. Fink, H. A. Ishani, A. Canales, M. T. Yaffe, K. Barrett-Connor, E. Orwoll, E. S. Shikany, J. M. Leblanc, E. S. Cauley, J. A. Ensrud, K. E. 25-Hydroxyvitamin D levels and cognitive performance and decline in elderly men. Neurology. Jan 5; 74 (1): 33-41.
  23. Waldstein, S. R. Wendell, C. R. Neurocognitive function and cardiovascular disease. J Alzheimers Dis. 20 (3): 833-42.
  24. Wilkins, C. H. Birge, S. J. Sheline, Y. I. Morris, J. C. Vitamin D deficiency is associated with worse cognitive performance and lower bone density in older African Americans. J Natl Med Assoc. 2009 Apr; 101 (4): 349-54.
  25. Wilkins, C. H. Sheline, Y. I. Roe, C. M. Birge, S. J. Morris, J. C. Vitamin D deficiency is associated with low mood and worse cognitive performance in older adults. Am J Geriatr Psychiatry. 2006 Dec; 14 (12): 1032-40.

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