Less sun, no worries: balancing a vitamin D deficit

The Northern Hemisphere experiences winter solstice today, Dec. 21, and Pacific Northwest residents look eagerly toward increasing minutes of daylight starting tomorrow. But during winter, while the sun is feeble, our vitamin D production naturally dips, too. 

UW Medicine diet and nutrition specialist Morgan Chojnacki explains that the sun’s ultraviolet rays interact with our skin to create vitamin D. This process is how people mostly generate their supply of the vitamin, which helps to strengthen bones. But during winter, the sun’s rays are too weak to trigger this process above the 37th parallel north (all of Washington state, and places including San Francisco, Denver, and St. Louis).

“A billion people worldwide are vitamin D deficient, including 40% of American adults,” said Chojnacki. “We can go stand on top of Mount Rainier and get sunburned right now, and we still wouldn't be able to produce vitamin D.”

Chojnacki says it’s difficult to get adequate vitamin D from our diets, but a few foods can help counterbalance the wintertime deficit:

  • Certain fish (salmon, herring, tuna, mackerel, sardines)
  • Fortified milk and dairy products
  • Fortified soy products
  • Eggs

She says common signs of vitamin D deficiency include muscle weakness and bone pain. More advanced symptoms can include depression, hair loss and slow-healing wounds.

Vitamin D supplements are available, and the National Institutes of Health recommends a volume of 600 IU daily. Chojnacki says taking 1,000 IU per day during the wintertime is OK for most people but suggests people speak with a physician before starting to supplement for vitamin D.

Chojnacki says vitamin D2 or D3 are good over-the-counter supplement options.

“[Vitamin] D3 is absorbed a little bit better, and your serum concentration levels stay higher,” said Chojnacki. “But if you're a vegetarian or vegan, vitamin D2 is the choice for you.”

Access broadcast-ready video with Chojnacki on wintertime vitamin D challenges and solutions.

UW Medicine