The days are growing shorter, temperatures are plummeting, and familiar tunes fill the air. Yes, even in the midst of an unprecedented pandemic, the holidays have come once again. Many around the country are looking to the holiday season for a rare spot of brightness, and a bit of familiarity amidst our uncertain present.

Even so, we should keep in mind that protecting our health and that of our loved ones is more important than ever this year during COVID-19. So it’s a great time to talk about a crucial, but often overlooked “bright idea” for good health: vitamin D.

Vitamin D boasts many benefits for the human body, from ensuring our bones stay strong to help support our immune systems. But wintertime often leaves many of us in northern latitudes with vitamin D deficiencies. Our bodies need sunlight to make the nutrient. So, when the days grow short and we cover our skin with warm clothes, most people need to supplement their diets with foods rich in vitamin D or supplements to get enough.

You’ve probably heard that vitamin D can help stave off depression in the winter months, but this year, more than ever, the immune system benefits are the foremost reason to be sure you’re getting enough of this crucial nutrient. Studies show many components of our immune system likely rely on vitamin D to function. In fact, the United Kingdom recently announced a plan to deliver vitamin D supplements to the elderly and others at higher risk of death from COVID-19. The decision reflects research showing that a lack of the nutrient is connected to a greater risk from symptoms of the coronavirus (Hernandez et al., 2020) (Carpagnano et al., 2020).

Foods for Vitamin D

You might imagine your body as a factory for making vitamin D — albeit one that may run short of raw material. When ultraviolet light from the sun hits our skin, it kicks off a chain reaction. With help from the liver and kidneys, cholesterol gets turned into vitamin D. Just a few hours in strong sunlight per week is usually enough for us to generate the vitamin D we need. But once winter hits, we’re far less likely to bare our skin outdoors. And for those of us who live north of the 37th parallel (a line that cuts through Utah, Colorado, Kansas, and Kentucky), winter sunlight just isn’t strong enough to put our bodies’ vitamin D assembly line in action. Instead, we need to get help from our diets.

Meat, eggs, and dairy all contain vitamin D, as well as foods that have been fortified — where the nutrient is added in artificially — like some orange juices. But oily fish such as salmon, halibut, and tuna are by far the best sources. Canned sockeye salmon has five times the vitamin D per serving as does whole milk, and nearly 15 times as much as eggs, according to the U.S. Dietary Guidelines Advisory Committee. Eating several servings of fish per week is the best way to make sure your diet contains enough vitamin D. Of course, vitamin D supplements accomplish much the same thing, making them another easy way to make sure your vitamin D intake meets guidelines.

For context, the National Institutes of Health recommends adults get 600 IU of vitamin D per day. One serving of canned sockeye salmon contains 585 IU, while a serving of cooked halibut contains 196 IU. An egg packs just 44 IU.

Dangers of Vitamin D Deficiency

Scientists estimate that as many as one billion people worldwide might be lacking adequate vitamin D, largely because they don’t get enough sunlight (Opinder Sahota, 2014). And studies over the years have linked low levels of the nutrient to a range of problems, starting in childhood. Children who don’t get enough vitamin D can develop rickets, a condition characterized by weak bones, and which can lead to abnormal development and fractures.

Vitamin D is necessary for our bodies to adequately incorporate calcium. Without it, bones are left fragile. That’s also why it’s important for the elderly to get enough vitamin D, as it can help stave off osteoporosis and prevent injuries. One study, for example, found a 58 percent reduction in bone fractures in people over the age of 65 who received daily vitamin D and calcium supplements (Dawson-Hughes et al., 1997). And vitamin D is thought to play a role in helping to maintain muscle strength, as well (Opinder Sahota, 2014).

Inadequate vitamin D has also been linked to higher levels of cancer, with a few studies finding a 30 to 50 percent increase in the risk of colon, prostate, and breast cancer. People with low vitamin D levels who get those cancers also suffer a higher rate of death. And another study found that increasing vitamin D levels with sunlight helped lower high blood pressure (Krause et al., 1998).

Some studies have also suggested vitamin D plays a role in mental health. A few researchers have shown that vitamin D deficiencies are common among people suffering from depression (Berk et al., 2007). But other researchers say more work needs to be done to find out exactly what the link between the two is, noting that some randomized, controlled trials of vitamin D supplements failed to produce any meaningful results (Dumville et al., 2014).

Vitamin D and Immunity

In addition to the many proactive ways vitamin D keeps us healthy, it also plays a role when our bodies go on the defense when we get sick.

Scientists still don’t fully understand the complex ways that vitamin D interacts with our immune system, but its essential role is clear. Some of the best evidence is found at the cellular level. Within the immune system, a number of cells have receptors for vitamin D, and several are even capable of synthesizing it themselves (Borges et al., 2011). This close relationship wouldn’t have evolved had vitamin D not been integral to immune function.

More specifically, researchers believe that vitamin D plays an important role linking the two halves of our immune system — the so-called “innate” side and the “adaptive” side. The innate immune system responds immediately to infections. The adaptive system learns to recognize invaders over time, helping the body mount a specialized defense against specific microbes while leaving harmless or beneficial ones alone.

More specifically, researchers have found that macrophages, the white blood cells that surround and destroy dangerous microbes, rely intimately on vitamin D for their functionality. Something similar seems to be the case with dendritic cells and T cells, which help our bodies recognize microbes and mount an immune response (Borges et al., 2011).

Studies looking at levels of vitamin D in sick people also offer strong signs of a connection. One 2017 review of 25 studies concluded that vitamin D helped cut down on respiratory infections, especially for those with already low levels (Martineau et al., 2017). Another study found that Japanese schoolchildren getting vitamin D supplements were 40 percent less likely to get a specific kind of flu (Urashima et al., 2010). (Read more: Vitamin D Likely Fights Lung-Focused Viral Villains)

And more recent studies of patients with COVID-19 have also discovered links between a lack of vitamin D and death from COVID-19. One study in Spain noted that an astonishing 80 percent of people hospitalized for COVID-19 had a vitamin D deficiency (Hernandez et al., 2020). And a different study from Italy indicated that a lack of vitamin D was associated with a higher risk of dying from the virus (Carpagnano et al., 2020).

This year, nothing’s guaranteed to ruin your holidays like a bout of sickness. So, as the weather gets crisp and the family gathers near (perhaps virtually), keep your spirits up and your health tip-top with an easy holiday helper — vitamin D.


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