Winter weather in northern climates calls for oversized sweaters, snow shovels, and much time spent indoors. In all, it’s a recipe for dipping vitamin D levels. 

Considering research estimates that upwards of 40 percent of Americans are deficient in vitamin D, we should all be more proactive about getting our recommended share of the ‘sunshine vitamin’. But that’s especially true during wintertime.

Our body can produce vitamin D when exposed to the sun’s ultraviolet B-rays (UVB), explains dietitian Jonathan Valdez, R.D.N., owner of Genki Nutrition. The issue is, if you live above a certain latitude, the sun isn’t strong enough in the winter to stimulate ample vitamin D production. In fact, research shows that people who live in Boston can’t produce a shred of D from the sun between November and February.

The Price Of Missing Out On Vitamin D In The Winter

In addition to supporting bone health, “vitamin D contains significant antioxidant abilities, improving cellular function and repairing DNA,” says naturopath Dr. Tricia Pingel, N.M.D., author of Total Health Turnaround. It also plays roles in energy, immune function, and mood.

As a result, having low levels of vitamin D can seriously impact on your health.

“Low levels of vitamin D are linked to mood issues, fatigue, changes in metabolism, suppressed immune function, and hormonal issues, amongst other things,” says Brittany Michels, M.S., R.D.N., L.D.N., a dietitian for The Vitamin Shoppe.

Read More: 7 Signs You Have A Vitamin D Deficiency

What vitamin D level is truly considered “healthy,” though, has been a bit up for debate. The National Institutes of Health identifies a level greater than or equal to 20 ng/ml as adequate. However, some experts disagree. “Once your vitamin D levels read above 40 ng/ml, you are in a better position when it comes to future health concerns,” says Pingel. Michels, meanwhile, recommends maintaining even higher levels of at least 50 ng/ml.

How Much Vitamin D Should You Supplement With In The Winter?

Considering what’s at stake if you fall short on vitamin D, which can be especially easy to do during the wintertime, a supplement may be an important part of your routine.

Just how much you should take, though, depends on a few factors.

1. Your current vitamin D status

An important first step here: understanding your starting vitamin D level, which your doctor can check with a simple blood test. If you tend to fall between 30 and 40 ng/ml, Pingel suggests you may need to double your current supplementation to surpass 40. Discuss with your doctor first and make a plan to recheck your levels after a few months.

Typical dosing for supplemental vitamin D3 ranges from 1,000 to 5,000 IU, and just how much you might need ultimately depends on what your starting level looks like. 

2. Your winter sun exposure

Since vitamin D is a fat-soluble vitamin, the body stores some of what it produces from sun exposure during the summer. However, vitamin D status may be depleted throughout the winter, after months of insufficient sun exposure, says Valdez.

If your level of sun exposure doesn’t change much throughout the year, you may not have the need for more vitamin D in the winter, according to Michels. However, if your level of exposure does change, you likely need to increase your supplementation during the winter months.

Live in the northern half of the United States? Research indicates that you can’t get the vitamin D you need from the sun this time of year, so upping your supplement might make sense.

3. Your skin tone

In addition, people with darker skin are limited in the amount of vitamin D the skin produces due to melanin content, says Valdez. One CDC report shows that Black people, for example, are 31 percent more likely to be deficient in vitamin D compared to other ethnic groups.

“Melanin is the pigment in our skin that is hypothesized to impact our vitamin D levels because it blocks the UV radiation required for the synthesis of vitamin D,” says Pingel. “This makes those with darker skin tones more susceptible to poor vitamin D synthesis through the skin.”

Depending on their baseline vitamin D status and diet, those with darker skin may need to increase their intake of the sunshine vitamin, she says.

4. Your age 

“Older adults experience a decline in their ability to make vitamin D through sunlight exposure and are at risk of not consuming enough vitamin D from diet,” says Valdez. As a result, people middle-aged and over may want to consider amping up their intake with a supplement, especially in the winter.

Read More: People Over 55 Need More Of These 5 Nutrients

5. Your overall health

Certain health concerns may require you to supplement with vitamin D year-round, and especially in the winter, particularly if you live in a northern climate or experience decreased sun exposure in the winter, notes Michels.

One example: “Those with digestive and immune issues tend to require higher levels of vitamin D to maintain normal levels,” she explains. The reason? Gut issues often lead to poor absorption.

Changes in mental health, having a hard time losing weight, poor sleep, increased frequency of sickness, low testosterone levels, and poor blood sugar management may also indicate that you need more vitamin D than you’re getting.

How to determine your exact vitamin D needs

If you’re concerned about your vitamin D levels, talk with your doctor about performing a simple blood test to find out where you’re at. From there, you can work with your provider or meet with a registered dietitian to evaluate your current routine and create a plan for meeting your needs through diet and supplementation.

“I normally recommend supplementing with 2,000 to 3,000 IU of vitamin D3 (which is the most absorbable form of vitamin D) per day if you get little sun exposure—and even more if you have low blood levels,” Michels says.

The Takeaway

Ultimately, depending on how the above factors apply to you, you very well might need to up your vitamin D intake with increased supplementation throughout the wintertime. 

“The majority of the nation requires an increase of vitamin D supplementation in the winter due to winter clothing and inadequate sun exposure—but it truly depends on the individual and their sun exposure habits,” Michels says. “If someone lives in sunny Hawaii and takes a 30-minute walk in the sun every day of the year, for example, their needs won’t change.” However, those who live in more northern regions that stay indoors more or have to bundle up during the winter most definitely need an increase of vitamin D.