Cognitive impairment Patient friendly summary

Several studies have found a link between vitamin D and better cognitive function.

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.

Find out more...

Do you want to find out more and see the research upon which this summary is based?  Read our detailed evidence summary on cognitive impairment.

Page last edited: 16 August 2011