Quantcast
Environmental News for a Healthier Planet and Life

Help Support EcoWatch

Why You Need More Vitamin D in the Winter

Health + Wellness
Yellow soft shell D-vitamin capsule held to the sun. Helin Loik-Tomson / iStock / Getty Images

By Margherita T. Cantorna

Winter is upon us and so is the risk of vitamin D deficiency and infections. Vitamin D, which is made in our skin following sunlight exposure and also found in oily fish (mackerel, tuna and sardines), mushrooms and fortified dairy and nondairy substitutes, is essential for good health. Humans need vitamin D to keep healthy and to fight infections. The irony is that in winter, when people need vitamin D the most, most of us are not getting enough. So how much should we take? Should we take supplements? How do we get more? And, who needs it most?


I am a medical microbiologist and immunologist who studies the functions of vitamin D in immune cells. My laboratory has been interested in figuring out why the immune system has vitamin D receptors that determine which cells can use vitamin D. In the immune system, vitamin D acts to improve your ability to fight infections and to reduce inflammation.

Where to Get Your Vitamin D

Vitamin D is called the sunshine vitamin since it is made in the skin after exposure to sun. The same UVB rays that cause a sunburn also make vitamin D. Sunscreen, darker skin pigmentation, clothing and reduced daylight in winter diminish the skin's ability to make vitamin D. The people who experience the biggest seasonal swings in vitamin D levels are fair-skinned individuals living in the northern regions of the U.S. and at higher latitudes around the globe where there is very little daylight in winter.

But those most at risk for low vitamin D levels are people of color and people living at higher latitudes. Dark-skinned individuals are more likely than fair-skinned individuals to be low for vitamin D year-round because the darker skin blocks the UVB rays from producing vitamin D. However, even in dark skinned individuals, vitamin D is lowest in the winter.

In the winter, in addition to high vitamin D food, adults should take additional vitamin D from foods and/or supplements to get at least 600 IU per day of vitamin D. People who have dark skin or avoid sunshine should eat more vitamin D year-round.

Vitamin D's Importance for Bones and Microbes

Originally, doctors thought that vitamin D was only important for bone health. This was because the vitamin D deficiency caused bone diseases like rickets in children and osteoporosis in adults. However, in the 1980s scientists discovered that immune cells had receptors for vitamin D.

My group's research has shown that vitamin D plays an important role in maintaining health in the gastrointestinal tract. Higher levels of vitamin D reduce susceptibility to inflammatory bowel disease and Crohn's disease, gut and lung infections in animals and people.

My colleagues and I have discovered that one of the ways vitamin D functions is by keeping the microbes in the gut healthy and happy. Vitamin D increases the number and diversity of microbes living in the gut, which together reduce inflammation throughout the body.

Low vitamin D levels are associated with inflammatory bowel disease in humans. Researchers have found that inflammatory bowel disease patients in Japan have more symptoms in winter than during other seasons.

Why is vitamin D more important in winter?

In the winter, humans are exposed to more infections and spend less time outside. Exactly how much vitamin D healthy adults should have is debated. Some authorities recommend from 200 IU per day to 2,000 IU per day. In the U.S., the Institutes of Medicine recommends 600-800 IU per day for adults, while the Endocrine Society states that optimal vitamin D status may require 1500-2,000 IU per day. In the winter, people have a reduced ability to make vitamin D when they go outside, so amounts of at least 600 IU per day of vitamin D from food or supplements would help maintain vitamin D status at summer levels.

But, just like many things, too much vitamin D can be harmful. Vitamin D toxicity does not result from too much sun or food. Because of the risk of skin cancer, dermatologists and other health professionals do not recommend unprotected sun exposure to boost your vitamin D. Instead they suggest supplements. But vitamin D toxicity can occur if an individual takes too many.

The experts that set the national intakes of vitamin D for the U.S. recommend that adult individuals take no more than 4,000 IU per day of vitamin D to avoid toxic side effects. Vitamin D helps you absorb calcium from your diet, but when vitamin D is too high, calcium levels in the blood go up and that can lead to kidney disease.

By consuming more vitamin D during the winter your gut microbes will be healthier and you'll be more resistant to infection and inflammation year-round.

Margherita T. Cantorna is a distinguished professor of molecular immunology at the Pennsylvania State University.

Reposted with permission from The Conversation.

EcoWatch Daily Newsletter

A bald eagle chick inside a nest in Rutland, Massachusetts. Massachusetts Division of Fisheries and Wildlife
A bald eagle nest with eggs has been discovered in Cape Cod for the first time in 115 years, according to the Massachusetts Division of Fisheries and Wildlife (Mass Wildlife), as Newsweek reported.
Read More Show Less
The office of Rover.com sits empty with employees working from home due to the coronavirus pandemic on March 12 in Seattle, Washington. John Moore / Getty Images

The office may never look the same again. And the investment it will take to protect employees may force many companies to go completely remote. That's after the Centers for Disease Control and Prevention (CDC) issued new recommendations for how workers can return to the office safely.

Read More Show Less
Frederic Edwin Church's The Icebergs reveal their danger as a crush vessel is in the foreground of an iceberg strewn sea, 1860. Buyenlarge / Getty Images

Scientists and art historians are studying art for signs of climate change and to better understand the ways Western culture's relationship to nature has been altered by it, according to the BBC.

Read More Show Less
Esben Østergaard, co-founder of Lifeline Robotics and Universal Robots, takes a swab in the World's First Automatic Swab Robot, developed with Thiusius Rajeeth Savarimuthu, professor at the Maersk Mc-Kinney Moller Institute at The University of Southern Denmark. The University of Southern Denmark

By Richard Connor

The University of Southern Denmark on Wednesday announced that its researchers have developed the world's first fully automatic robot capable of carrying out throat swabs for COVID-19.

Read More Show Less
Jackson Family Wines in California discovered that a huge amount of carbon pollution was caused by manufacturing wine bottles. Edsel Querini / Getty Images

Before you pour a glass of wine, feel the weight of the bottle in your hand. Would you notice if it were a few ounces lighter? Jackson Family Wines is betting that you won't.

Read More Show Less
The SpaceX crew capsule will launch out of Cape Canaveral, Florida. SpaceX

After a minor setback, a new era in space travel and tourism is set to launch this weekend.

Read More Show Less

Trending

A former Federal Reserve board of governors member on Thursday called on her former colleagues to stop using Covid-19 relief funds to bail out the "dying" fossil fuel industry. Douglas Sacha / Getty Images

By Eoin Higgins

A former Federal Reserve board of governors member on Thursday called on her former colleagues to stop using Covid-19 relief funds to bail out the "dying" fossil fuel industry, calling the decision a threat to the planet's climate and a misguided use of taxpayer money.

Read More Show Less