Seasonal insomnia may be driven by vitamin D deficiencySeasonal insomnia typically strikes at about this time of year. As the days get shorter, we’re exposed to shorter periods of sunlight, which can alter circadian rhythms and interfere with sleep.

A related problem has to do with our need for vitamin D, which may not be met in low sunlight conditions. Recent publications explore the effects of low levels of vitamin D on sleep, making supplements a good option in the cold weather.

A Relationship Between Sleep and Vitamin D

It’s well established now that lack of exposure to sunlight has a negative effect on sleep. Interest in the relationship of vitamin D to sleep is relatively new, yet preliminary evidence suggests that low levels of D are associated with short sleep duration, a frequent complaint of people with insomnia. A recent meta-analysis of studies of vitamin D deficiency and sleep disorders also found an association between low levels of D and poor sleep quality.

Levels of vitamin D fluctuate seasonally. Our bodies make most of the vitamin D we need when our skin is exposed to sunlight, and typically there are fewer opportunities for sunlight exposure in the colder months of the year. Thus insufficient vitamin D could be a factor in seasonal insomnia.

Vitamin D Supplements: Will They Improve Sleep?

While a few studies document improved sleep as a result of higher levels of vitamin D, a causal relationship between vitamin D supplementation and better sleep has not been definitively established. However, for a host of health reasons including sleep — avoidance of infectious, autoimmune and neurological diseases, as well as neuromuscular disorders and increased pain sensitivity — vitamin D deficiency is a condition we should try to avoid.

It’s a good idea to pay attention to recommended dietary allowances — expressed in international units (IU) per day — especially in the wintertime. They were established by the Institute of Medicine based on vitamin D’s importance to the development and maintenance of healthy bones. Subsequently the Endocrine Society established recommended dietary allowances for people at risk for vitamin D deficiency. Here’s a table showing both sets of guidelines for daily intake of vitamin D:

Infants Ages 1–18 years Ages 19–70 years Ages 71 & older
Institute of Medicine 400 IU/day 600 IU/day 600 IU/day 800 IU/day
Endocrine Society 400-1000 IU/day 600-1000 IU/day 1500-2000 IU/day 1500-2000 IU/day

Foods Containing Vitamin D

Up to 80% of our D requirement may come from the complex metabolic processes triggered with exposure of the skin to sunlight. But we also get vitamin D from a limited number of foods. Some foods naturally contain D and other foods are fortified with it. Here are some common foods containing vitamin D and approximate amounts:

  • 3.5 oz salmon, fresh (wild): 600–1,000 IU
  • 3.5 oz salmon, fresh (farmed): 100–250 IU
  • 3.5 oz salmon, canned: 300–600 IU
  • 3.5 oz sardines, canned: 300 IU
  • 3.5 oz mackerel, canned: 250 IU
  • 3.5 oz tuna, canned: 236 IU
  • 3.5 oz shiitake mushrooms: 100 IU
  • 1 egg yolk: 20 IU
  • 3.5 oz beef liver, braised: 12–30 IU
  • 8 oz fortified milk or yogurt: 100 IU
  • 8 oz fortified orange juice: 100 IU
  • 3 oz fortified cheese: 100 IU

Breakfast cereals and soy products are also often fortified with vitamin D.

At Risk for Vitamin D Deficiency

You’re more likely to have low levels of vitamin D in these conditions:

  • You get little exposure to sunlight. This may occur if you live in a northerly latitude, spend all or most of your time indoors, habitually wear clothing covering your entire body or cover up with sunscreen all the time. (An SPF of 30 or higher, which confers important protection from cancer, decreases vitamin D synthesis in the skin by more than 95%.)
  • You have dark skin. Dark skin confers natural protection from harmful radiation from the sun but also makes it harder to synthesize vitamin D. Longer periods of sun exposure are required for sufficient vitamin D production to occur.
  • You’re vegan. Most natural sources of vitamin D are animal based.
  • You’re obese. Individuals with a body mass index of 30 or higher often have low blood levels of vitamin D.
  • You’re pregnant or lactating. Pregnant and lactating women may have decreased levels of vitamin D as well.
  • You’re older and have a history of falls and/or fractures. Older adults are somewhat less efficient at synthesizing vitamin D via sunlight exposure.

Vitamin D Supplementation

To remedy low levels of vitamin D, or to maintain adequate levels throughout the winter, take a vitamin D supplement. Take your daily supplement with a meal containing fat, as this will increase vitamin D absorption.

Supplementation and adequate exposure to sunlight (or bright light supplied by a light box) at the approach of the holidays and through the winter may help to protect you from the bane of seasonal insomnia.

Posted by Lois Maharg, The Savvy Insomniac

Lois Maharg has worked with language for many years. She taught ESL, coauthored two textbooks, and then became a reporter, writing about health, education, government, Latino affairs, and food. Her lifelong struggle with insomnia and interest in investigative reporting motivated her to write a book, The Savvy Insomniac: A Personal Journey through Science to Better Sleep. She now freelances as an editor and copy writer at On the Mark Editing.


  1. I’ve read that you should take your vitamin D supplement in the morning, since it is associated with sunlight, and taking it at night may increase insomnia.



  2. Hi Jenn,
    I can see where someone might get the idea, because of the association between vitamin D and sunlight, that taking vitamin D would tend to wake you up rather than put you to sleep. But no research I’ve ever come across would support that assertion. As vitamin D is fat soluble, the best time to take a supplement is with a meal containing fat, whether that’s typically breakfast, lunch or dinner.
    Thanks for writing in, as others may have the same concern.



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