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Seeing the Light on Vitamin D

The nutrient is essential for brain function, yet most Americans don’t get enough.

It’s winter. Do you know what your vitamin D status is?

If you’re like most Americans, your level is suboptimal (under 30 nanograms/mL) if not frankly deficient (under 20 ng/mL), and you don’t get enough of the nutrient from food to meet current standards, which scientists increasingly believe are anemic to begin with. Come winter, if you live north of Atlanta, there’s not even the possibility of getting enough sun—the biggest source of vitamin D, which is produced in skin exposed to
UVB rays— to meet your needs.

It’s now clear how much that matters. Twenty years ago, everyone thought that, as the body’s chief calcium-regulating hormone, vitamin D’s contribution to health was the making of strong bones. That may now be the least of it.

Ongoing studies show that the nutrient plays a regulatory role in almost every system in the body. And its most notable actions may be in the brain. There, researchers find, it has an array of effects, from stimulating the growth of nerve cells to preserving memory and executive function, all the while clearing out the toxins implicated in Alzheimer’s disease. And no one has a firm fix on how much it takes to underwrite all its newly discovered talents in maintaining brain health.

Vitamin D deficiency not only puts older adults at risk for cognitive decline and dementia, reports Michael Holick, it has “serious long-lasting consequences for mental health” throughout life. In utero D controls the necessary pruning of nerve cells as the brain develops.

A professor of medicine at Boston University and probably the world’s leading expert on vitamin D, Holick finds that deficiency of the vitamin is widespread among all age groups, especially in industrialized countries. Contrary to expectations, those most at risk are young adults: They’re always indoors, working.

Cognitive function doesn’t start heading south at age 65. It takes decades for neural changes to manifest clinically. That’s why University of Kentucky researchers chose to study middle-aged mice, considered models of human aging. Only those getting high D doses—almost twice the current recommendation for humans—aced the subtlest of water maze tests, the team reports in the Proceedings of the National Academy of Sciences.

The researchers found that vitamin D facilitates memory consolidation by boosting the strength of nerve signals: It stimulates gene expression of molecules essential to neurotransmission. It also preserves the myelin sheath around nerve fibers.

Low vitamin D levels accelerate memory loss, University of California at Davis researchers found in a study of nearly 400 older men and women followed for five years. Among those with subpar levels of the vitamin, episodic memory and executive functioning declined two to three times faster than among those with normal levels. Both the speed and degree of cognitive decay surprised the scientists.

At a 2013 vitamin D summit in Boston, experts from around the world suggested that the stage for cognitive decline may be set prenatally; animal studies show that prenatal vitamin D deficiency disrupts brain development and impairs later brain functioning. Variations in incidence of schizophrenia by season and place of birth implicate prenatal vitamin D deficiency in psychosis as well.

The RDA for vitamin D is 600 International Units for people between ages 1 and 70; it’s 800 IU for those over 70. Even at the recommended dose, Holick reports, 76 percent of new mothers and 81 percent of newborns are D-deficient. He believes that 4,000 IU of vitamin D3 is optimal during pregnancy. He downs 4,000 units a day, “and that’s what I prescribe for all my patients. They tell me all their winter aches and pains disappear.”

Vitamin D in the Brain

  • Directly protects cells in the hippocampus, essential for memory consolidation and spatial navigation
  • Regulates differentiation and maturation of neurons by stimulating production of nerve growth factors
  • Attenuates accumulation of amyloid-beta, the toxic protein involved in Alzheimer’s disease
  • Acts as a potent antioxidant by inhibiting production of free radicals
  • Lowers risk of stroke and resulting impairment
  • Regulates levels of anti-inflammatory agents
  • Regulates genetic expression of neurotransmitters including dopamine, acetylcholine, and serotonin
  • Maintains mood

A Vitamin of Many Talents

  • Maintains muscle function
  • Regulates apoptosis
  • Reduces inflammation
  • Moderates immune function
  • Controls nerve function
  • Promotes calcium absorption
  • Builds bone
  • Modulates cell growth

D Facto

  • Vitamin D is produced in the epidermal (topmost) skin cells exposed to ultraviolet B rays of sunlight; to be biologically active, it is converted first by the liver, then by the kidneys.
  • Very few foods contain vitamin D. Salmon and sardines are richest in the nutrient.
  • Vitamin D deficiency has been rising since the 1980s, largely due to use of sunscreens, which block vitamin D production in skin.
  • Vitamin D deficiency is now considered a risk factor for development of diabetes.
  • Vitamin D affects expression of many genes linked to calcium, autoimmune disorders, and cardiovascular disease.
  • Hundreds of genes in the brain alone are regulated by vitamin D.
  • Most tissues and cells in the body have a receptor for vitamin D.
  • Long-term vitamin D supplementation has been shown to lower all-cause mortality.
  • A blood test to measure vitamin D levels is usually not done routinely; at your next medical checkup, ask your doctor to include the measurement.

Credit: Forest road by Grisha Bruev/Shutterstock