It’s officially that time of year. The time where we swap swimwear for sweaters and iced lattes for steamy PSLs. As summer gives way to fall and winter, we’ll also get less and less sunlight. Sure, this can give off real cozy vibes for a night in (scented candles and a movie, anyone?), but a lack of sun can also affect our well-being. Case in point: Getting enough vitamin D during shorter, darker days can be a challenge.

Here’s why getting less of the nutrient can lead to health issues and how to get more vitamin D in fall and winter.

Why you get less vitamin D during shorter, darker days

As you might know, sunlight exposure triggers our bodies to produce vitamin D. “Since our skin requires direct sunlight for this process to take place, shorter days can reduce how much vitamin D we produce during the winter months,” says Jacqueline Gomes, RD, a registered dietitian based in Warren, New Jersey. “Our vitamin D levels tend to peak in late summer and early fall, so our vitamin D stores can start to deplete just before the winter months.”

Here’s a closer look at how it works: “Ultraviolet B (UVB) rays penetrate the outer layer of your skin and convert a cholesterol derivative into vitamin D3, which then travels to the liver and kidneys to be further processed into active vitamin D,” explains Raj Singh, MD, FACP, FASN, a primary care doctor based in Las Vegas.

Vitamin D created by this process may last at least twice as long in the blood as vitamin D you get from a supplement, according to a 2023 report in the Brazilian journal Revista Paulista de Pediatria¹. But the weather forecast plays a role. “On a clear day, your skin can produce a substantial amount of vitamin D in a relatively short period,” Dr. Singh says. “On a cloudy day, the process still occurs, albeit at a slower rate because clouds filter a significant amount of light.”

The temperature of your skin might also play a role here. According to Harvard Health Publishing, warm skin produces vitamin D more efficiently than cool skin. This means you’ll make more vitamin D on a hot day vs. a cool one.

What happens to your body when you get less vitamin D 

Vitamin D plays a major role in our overall health. In fact, vitamin D receptors are in nearly all cells of our body, per a July 2017 paper in Annals of the New York Academy of Sciences². The essential nutrient plays a role in regulating the immune system, relaxing blood vessels, and supporting heart and bone health, and it also may help prevent certain cancers, according to Dr. Singh and Gomes.

Signs of low vitamin D include getting sick more often and feeling tired. Over time, not getting enough can lead to a deficiency, says Dr. Singh, which may be linked to long-term health issues such as:

• Increased gut inflammation (such as colitis and gut microbiome imbalance)
• Decreased bone health and risk of bone loss (leading to osteopenia and osteoporosis)
• Increased risk of cardiac problems (due to blood vessel stiffness and worsening of heart failure)
• Asthma and chronic lung disease flare-ups (likely related to increased inflammation)
• Fertility issues
• Increased pain in people with fibromyalgia and other chronic inflammatory conditions

Many people with low levels of vitamin D report symptoms of increased pain, fatigue, bone pain, gait instability due to muscle weakness, muscle spasms, and sometimes tingling and numbness throughout the body, Dr. Singh says.

How much vitamin D to get per day

If vitamin D is so important, how much of it should we actually be getting per day? The recommended daily amount (RDA) is 600 International Units (IU) or 15 mcg for adults, per the National Institutes of Health (NIH). Children ages 1 to 18 should get the same amount, while adults over 70 need a bit more—20 mcg (800 ICU) per day.

Tips to get more vitamin D when there’s less sunlight

Thankfully, the sun isn’t your only support system when it comes to getting more vitamin D in the fall and winter. Here are some strategies to try now, so your vitamin D levels stabilize by the time peak cold, dark days arrive.

1. Load up on vitamin D-rich foods

It can be difficult to find sufficient amounts of vitamin D in food alone, but not impossible. Some foods high in vitamin D include the following:

• Fatty fish: A 3.5-ounce serving of salmon has 526 IU of vitamin D, while light-canned tuna has 269 IU of vitamin D per 3.5-ounce serving. Sardines and herring are also great sources of this nutrient. “Add more fish to your weekly menu with options like salmon and sautéed mushrooms for dinner, or a tasty tuna salad for lunch to keep your vitamin D levels up,” Gomes says.
• UV-exposed mushrooms: Mushrooms are unique in that they are the only sufficient plant-based source of vitamin D—but only if they’re exposed to sunlight rather than grown in the dark. “They are similar to us in that they produce vitamin D when UV rays hit them,” Gomes says. Next time you’re grocery shopping, look for the brand Monterey Mushrooms, which are grown under UV light.
• Egg yolks: Two large egg yolks have 9 percent of your daily value of vitamin D. Gomes suggests starting your day with a protein-packed egg and mushroom omelet to get in more of the nutrient.
• Milk: Cow’s milk in the U.S. is almost always fortified with vitamin D. Some plant-based milk alternatives also have vitamin D added to mimic the nutritional profile of dairy milk. Just make sure to check the nutrition facts label on your milk to see if it has D. “For a snack, consider a smoothie prepared with a vitamin D-fortified milk or milk alternative,” Gomes suggests.

2. Consider a supplement

If you find out you’re vitamin D deficient after getting blood work done, your doctor might suggest taking a supplement. To help restore your levels, you’ll need around 6,000 IU of vitamin D3 daily (or 50,000 IU weekly) for eight weeks, per the NIH. Then, once you reach a healthy level, you can maintain it by taking 1,000 to 2,000 IU daily.

When you’re shopping for a supplement, look for a brand that’s certified by a third party, like NSF or USP. “Third-party testing indicates that an independent lab with no connection to the brand has verified the supplement quality and accuracy of its labeling,” Gomes says. We especially like Thorne and Nature Made supplements.

3. Get outside during peak sunlight to maximize exposure

Even on a cloudy or rainy day, the sun’s rays are strongest between 10 a.m. and 4 p.m., so you’ll want to take a break and step outside during that window. One way to achieve this is by taking a 20-minute walk during lunchtime, which Gomes says can benefit your vitamin D production and mental health. “Aim to get out at least three days per week,” she adds.

Another tip? Try swapping out your treadmill time for an outdoor run instead, adds Gomes. This can also help raise vitamin D levels, even if you’re running in cloudy or rainy weather, or wearing long sleeves when it’s cool.

4. Try a sun lamp

The research on this is limited, but some studies suggest using a sun lamp—which gives off UV rays similar to sunlight—could help you produce more vitamin D. According to an older October 2007 study in Photodermatology, Photoimmunology & Photomedicine³, sun lamps can be especially helpful for people with fat absorption problems, or those with cystic fibrosis or short-bowel syndrome, who can’t absorb enough vitamin D from their diets. That said, more research is needed to fully confirm these benefits.

People living in areas with little sunlight may benefit from using these lamps for short periods at a time, Dr. Singh says. “However, it’s crucial to wear eye protection when using sun lamps to shield the retina from harmful ultraviolet rays,” he adds.

BTW, sun lamps (and light therapy, light boxes, and other non-UV emitting devices) aren’t to be confused with UV lamps—which do emit UV rays, per the Cleveland Clinic. Light therapy can be helpful in easing seasonal affective disorder during the darker months, per the Mayo Clinic.

If you want to try a sun lamp, ask your doctor if it’s the right move for you and if they have a specific brand they recommend.

When to see a doctor about vitamin D deficiency

For most people, it’s inevitable that vitamin D levels will dip a little during shorter, darker months—especially if you live in a place with colder weather. Trying some of the above strategies can help even out your levels and prep you for the winter ahead.

But if you’re concerned about vitamin D going too low (or if you notice symptoms like muscle pain, weakness, or tingling in your hands and feet), head to your doctor for a blood test. While your doctor can order blood work at any time, Dr. Singh recommends getting it done at least once a year with your primary care doctor.

From there, if the test shows you’re low on vitamin D, you can work with your doctor to figure out a treatment plan that’s right for you.

—reviewed by Jennifer Gilbert, MD, MPH