Quantcast

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

We need our government to do everything it can to stop PFAS contamination and exposure from wreaking havoc in communities across the country. LuAnn Hun / Unsplash

By Genna Reed

The EPA announced last week that it is issuing a preliminary regulatory determination for public comment to set an enforceable drinking water standard to two of the most common and well-studied PFAS, PFOA and PFOS.

This decision is based on three criteria:

  1. PFOA and PFOS have an adverse effect on public health
  2. PFOA and PFOS occur in drinking water often enough and at levels of public health concern;
  3. regulation of PFOA and PFOS is a meaningful opportunity for reducing the health risk to those served by public water systems.
Read More
Charging EVs in Stockholm: But where does a dead battery go? Ranjithsiji / Wikimedia Commons

By Kieran Cooke

Driving an electric-powered vehicle (EV) rather than one reliant on fossil fuels is a key way to tackle climate change and improve air quality — but it does leave the old batteries behind as a nasty residue.

Read More
Sponsored
U.S. Secretary of the Treasure Steven Mnuchin arrives for a welcome dinner at the Murabba Palace in Riyadh, Saudi Arabia on Feb. 22, 2020 during the G20 finance ministers and central bank governors meeting. FAYEZ NURELDINE / AFP via Getty Images

Finance ministers from the 20 largest economies agreed to add a scant mention of the climate crisis in its final communiqué in Riyadh, Saudi Arabia on Sunday, but they stopped short of calling it a major economic risk, as Reuters reported. It was the first time the G20 has mentioned the climate crisis in its final communiqué since Donald Trump became president in 2017.

Read More
Aerial view of Parque da Cachoeira, which suffered the January 2019 dam collapse, in Brumadinho, state of Minas Gerais, Brazil — one of the country's worst industrial accidents that left 270 people dead. Millions of tons of toxic mining waste engulfed houses, farms and waterways, devastating the mineral-rich region. DOUGLAS MAGNO / AFP / Getty Images

By Christopher Sergeant, Julian D. Olden

Scars from large mining operations are permanently etched across the landscapes of the world. The environmental damage and human health hazards that these activities create may be both severe and irreversible.

Read More
Participants of the climate demonstration Fridays for Future walk through Hamburg, Germany on Feb. 21, 2020. Axel Heimken / picture alliance via Getty Images

By Andrea Germanos

U.S.-based youth climate activists on Friday drew attention to the climate protest in Hamburg, Germany, where organizers said roughly 60,000 people took part, and hoped that Americans took inspiration from their European counterparts.

Read More