Playing Defense: Boost More Than Just Your Immune System This Winter

Gateway Garden Center

by Sasha Reddy

Cold season is well underway. Many folks have spent the past three months or so going through the yearly rigmarole of seeking out ways to tighten their body’s defenses against the flu and other illnesses. This past year, amidst the COVID-19 pandemic and the onset of winter, there has been added buzz around one particular immune-boosting solution: vitamin D.

Vitamin D, also known as the sunshine vitamin, has been touted as one of the most vital nutrients for protecting us against illness. Preliminary research has even found a relationship between vitamin D deficiency and the rate of COVID-19 contraction. One UK-based study analyzed the number of coronavirus cases and deaths per million across 20 European countries during the first wave of the virus in Spring, 2020. The study found a negative correlation between vitamin D levels and COVID-19 contraction; in countries with lower rates of vitamin D deficiency, fewer coronavirus cases were seen. Though we can’t conclude from this research that vitamin D is the COVID-repellent we’ve been seeking, the research results are encouraging.

Photo of a hand holding up a translucent yellow pill in front of the sun.

Where do we get Vitamin D?

  • Sun – Our bodies are equipped to produce vitamin D when we are exposed to ultraviolet light. Unfortunately, sunlight exposure we get while indoors (like light coming in from a window) does not help us synthesize vitamin D.
  • Supper – It is extremely difficult to get the amount of vitamin D we need from nutrition alone, as it doesn’t occur naturally in many foods. Fish such as trout and salmon contain the most vitamin D naturally, though products like cheese and cow’s milk are often fortified with vitamin D.
  • Supplements – You can buy supplements of both forms of vitamin D (D2 and D3). Some research suggests that D2 is less effective at increasing the vitamin D levels in your blood, but both types will get the job done.

It’s an Uphill Battle

Unfortunately, when it comes to preventing infection in the wintertime, we’re already at a disadvantage. Humans and certain animals synthesize the vitamin D hormone as a response to direct sunlight exposure – that much is pretty well-known. What’s also well-known is that we get the least amount of UV exposure during the winter months, both because of the reduced number of daylight hours and because of the extra time spent indoors. On top of that, during fall and winter, when the average temperature goes way down, the flu virus is able to survive while airborne for longer periods of time. This gives the virus more time to spread from person-to-person, resulting in a seasonal spike in flu cases year after year. In other words, the time of year when we most desperately need Vitamin D to fight off the flu and other viruses just so happens to also be the time when we are likely not getting enough.

Now, just because opportunities to make vitamin D become limited in the wintertime doesn’t automatically mean that you are deficient. A blood test is required to gauge the body’s vitamin D saturation. Mayo Clinic recommends that most people get 600 international units (IU) of vitamin D daily, though infants below age one and seniors age 70 and above only need about 400 IU each day. There are a lot of factors that affect our ability to create vitamin D, so sitting in the sun for a while each day won’t guarantee that you’re getting enough. So what other lines of defense can we use?

Three athletes leaning down to reach for a kettlebell on the ground immediately in front of each person. Photo is taken from the knees down.

Fitness Fights the Flu

Regular exercise has proven to be one of the backbones of a healthy immune system, though we don’t entirely understand how or why. Some researchers theorize that exercise, which improves circulation, allows antibodies and white blood cells to travel through the body faster, resulting in a speedier response to pathogens. Other studies suggest that the heavy breathing that results from vigorous physical activity actually helps clear bacteria out of our airways. Either way, there’s a strong case to be made for maintaining an active lifestyle to help shield yourself from various infectious diseases.

The World Health Organization recommends at least 150 minutes of moderate-intensity physical activity throughout the week, or at least 75 minutes of vigorous exercise throughout the week.

Close-up photo of an individual snowflake attached to a larger collective of snow.

Goodbye, Winter Blues

From all of this information, we can make a few conclusions: if you can’t naturally produce enough Vitamin D to protect you this flu season, regular exercise can help build up your immune system to help make up for it. Research even suggests that regular exercise and sufficient vitamin D levels may help keep you COVID-free, though more studies are needed to verify. But there’s another area in which both vitamin D and regular exercise can help you.


As many as ten percent of Americans experience Seasonal Affective Disorder (SAD), a type of depression that occurs in the fall and winter months. Various studies have linked SAD and its symptoms to vitamin D deficiency, suggesting that the lack of sun exposure we receive in the wintertime and the lack of vitamin D synthesis that results actually causes our winter blues. This has led some scientists to believe that proper vitamin D levels in the blood can help alleviate SAD symptoms. Similarly, exercise stimulates the release of serotonin, dopamine, and other “happy” hormones and chemicals, which helps combat not just the winter blues but depression more broadly.

The past year, we’ve been forced to fight difficult battles on multiple fronts. We’ve become ragged from defending ourselves not just against COVID-19, but also against the loneliness and gloom that has come with isolating ourselves from the world. Making sure you’re getting the right levels of vitamin D and participating in regular exercise are just two of the ways you can strengthen your defenses against these enemies. Though neither one is the be-all, end-all solution, the more lines of defense we have, the better off we’ll be.


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