Improving cognitive function and sleep quality in older adults with higher-dose vitamin D supplementation

Most of the body’s cells and tissues have receptors for vitamin D, including those in the brain and nervous system. A study from Emory University in the United States suggests that older adults who take a high daily dose of vitamin D perform 13 percent better on cognitive tests compared with older adults who do not take a high daily supplement. The researchers therefore assume that high-dose vitamin D supplementation may help reduce early stages of cognitive decline, early signs of dementia, and sleep problems.

Cognitive decline includes a gradual loss of mental abilities such as memory, language, concentration, overview, and orientation. Mild cognitive impairment represents a stage between normal aging processes and early dementia. Furthermore, around half of those with mild cognitive impairment experience sleep problems, which over time increases the risk of Alzheimer’s disease, the leading cause of dementia.
Several mechanisms seem to be involved, such as neuroinflammation and the accumulation of harmful proteins in the brain that may explain a possible connection between cognitive decline and sleep problems.
Diet and lifestyle also have a major impact on cognitive function and sleep quality. However, it has been unclear how significant a role vitamin D plays in cognitive function, particularly among people with mild cognitive impairment and sleep problems.
The purpose of the new study, conducted at Emory University in the United States, was therefore to investigate this connection more closely. The study included 54 older participants of both sexes with an average age of 67. All participants had been diagnosed with or were suspected of having mild cognitive impairment. The participants’ degree of cognitive impairment was assessed using a test called the Montreal Cognitive Assessment, which covers language, memory, orientation, abstraction, and various practical tasks. The participants’ sleep quality and sleep patterns were assessed using specific scales. The participants were then divided into two groups. One group was instructed to take a high daily dose of vitamin D (125 micrograms, equivalent to 5,000 IU), while the other group served as a control group. The researchers also accounted for confounding factors such as age, sex, BMI, and education.
The study revealed the following:

• The group taking the high daily dose of vitamin D had a 13 percent higher score on the Montreal Cognitive Assessment compared with the group that did not take vitamin D supplements
• Lower doses of vitamin D had no significant effect on the overall cognitive score.

According to the researchers, this is the first study to evaluate the association between vitamin D supplementation and cognitive abilities in older adults who have both mild cognitive impairment and sleep problems. The researchers therefore assume that higher-dose vitamin D supplementation is associated with better cognitive abilities in this population.
The researchers also point out that the official US recommendations for vitamin D are at least 15 micrograms for people ages 50–70 and at least 20 micrograms for people over age 70. These official recommendations are similar to the Danish recommendations. However, as noted above, the participants in the study received a much higher dose (125 micrograms), which is also above the safe upper limit of 100 micrograms per day.
Although the researchers are calling for further studies in this area, there appears to be considerable evidence that the official recommendations for vitamin D for older adults, as well as the upper intake limits, should be adjusted. The new study was published in Sleep Medicine.

The importance of vitamin D for the brain and sleep quality

• Most cells and tissues in the brain, including the hypothalamus and hippocampus, have receptors for vitamin D
• Vitamin D regulates a wide range of genes and neurotransmitters
• Vitamin D plays a role in the activation and synthesis of tryptophan, a precursor of serotonin and the sleep hormone melatonin
• Vitamin D reduces neuroinflammation, which causes oxidative stress and cellular damage through free radicals
• Vitamin D helps protect the blood-brain barrier.

Important interaction between vitamin D and magnesium

For your information, there is an important interaction between vitamin D and magnesium, as magnesium plays a role in the enzymatic processes that activate the form of vitamin D we obtain from sunlight or supplements. In the following article, you can read more about the importance of magnesium for the nervous system and sleep quality, and how magnesium deficiency also increases the risk of dementia and Alzheimer’s disease.

• There is a link between Alzheimer’s disease and magnesium deficiency

References:

Sirui Zhou et al. Vitamin D supplement intake is associated with better cognition in persons with sleep disturbance and mild cognitive impairment. Sleep Medicine. 2026

Emory University. This common vitamin was linked to 13 % better cognitive scores. ScienceDaily 2026

Shreeya S Navale et al. Vitamin D and brain health: an observational and Mendelian randomization study. The American Journal of Clinical Nutrition, 2022