Winter changes more than the weather. Shorter days, heavier clothing, and more time indoors can reduce the amount of vitamin D the body makes from sunlight, especially at higher latitudes.
That matters because vitamin D helps the body absorb calcium, supports muscle movement and immune defense, and contributes to brain function, although supplements have not been shown to prevent or ease depression.
The good news is that maintaining vitamin D does not require hours in the sun or a shelf full of pills. The most practical approach combines safe outdoor time, vitamin D-rich foods, fortified staples, regular exercise, and medical advice before supplements. There is one important caution, though, because more vitamin D is not automatically better.
Step outside without chasing a tan
A lunch-break walk or a few minutes outdoors can build natural light and movement into a cold-weather routine. Your skin may make some vitamin D outside, but the amount varies with season, latitude, cloud cover, age, skin tone, and how much skin is exposed.
What about sitting beside a sunny window? It may feel good on a gray day, but sunlight through glass does not make the skin produce vitamin D. In deep winter, outdoor light may also be too weak in some places to provide much of the nutrient.
That does not mean skipping sunscreen or seeking a tan. The American Academy of Dermatology advises healthy adults to rely on food and fortified products for vitamin D because ultraviolet radiation raises skin cancer risk. Keep normal sun-protection habits while enjoying the fresh air.
Put fatty fish on the menu
Salmon, sardines, trout, tuna, and mackerel are among the best natural food sources of vitamin D. A practical target for many adults is about two fish meals a week, or roughly 8 ounces total, while choosing varieties that are lower in mercury.
This habit does double duty. Fish also provides high-quality protein and beneficial fats, so a salmon dinner or sardines on toast can strengthen the overall diet while adding vitamin D. Canned and frozen options count, which matters when the grocery bill is tight.
Variety is useful, especially with tuna and mackerel, because mercury levels differ by species. The U.S. Food and Drug Administration offers a “Best Choices” list that includes salmon, sardines, Atlantic mackerel, canned light tuna, and trout.
Check labels for fortified foods
“Fortified” simply means a nutrient was added during manufacturing. In the United States, nearly all milk is fortified with about 120 international units of vitamin D per cup, and many soy, almond, and oat drinks contain a similar amount.
Some yogurts, breakfast cereals, orange juices, and margarines also contain added vitamin D. But not every product does. The Nutrition Facts label is the quickest way to compare brands and see how much one serving contributes.
In practical terms, a fortified drink with breakfast can quietly close part of the winter gap. It is not flashy, but it is easy to repeat every day. That consistency often matters more than a one-time health kick.
Keep muscles and bones working
Exercise does not create vitamin D, so it cannot replace food, a supplement prescribed for deficiency, or medical treatment. But it supports the same body systems that vitamin D helps, especially muscle strength, balance, and bone health.
The National Institutes of Health puts it plainly when describing vitamin D. “Your muscles need it to move.” A shortage can contribute to muscle weakness and bone pain, while long-term shortages of vitamin D and calcium can leave bones more fragile.
The Centers for Disease Control and Prevention recommends at least 150 minutes of moderate activity each week for adults, plus muscle-strengthening work on two days. Brisk walks, stairs, resistance bands, and weights all count. The point is consistency, not a heroic January workout.
Do not self-prescribe supplements
Most adults ages 19 through 70 need 600 international units of vitamin D a day, while adults 71 and older need 800. Dr. Marie Demay of Harvard Medical School and Massachusetts General Hospital chaired the panel behind the Endocrine Society’s 2024 guideline.
It found that healthy adults under 75 are unlikely to benefit from routinely taking more than the recommended daily amount, while some other groups may need different guidance.
People who rarely go outdoors, have darker skin, are older, have obesity, underwent gastric bypass surgery, or live with conditions that reduce fat absorption may face a higher risk of low vitamin D. Children, pregnant people, adults over 75, and some people with prediabetes may also need more individualized advice, so a clinician should decide whether testing or a tailored dose makes sense.
Too much vitamin D can cause nausea, weakness, dehydration, kidney stones, an irregular heartbeat, and kidney failure. For adults, the general upper limit is 4,000 international units a day from all sources unless a health professional prescribes more to treat a deficiency.
The official vitamin D guidance was published on the National Institutes of Health Office of Dietary Supplements.
