Of the many nutrients that are vital for our everyday health, vitamin D is one of the most talked about due to its immune-supporting benefits. Known as the “sunshine vitamin,” vitamin D is a tricky nutrient because it’s not found in many foods. In fact, our main source of vitamin D is the sun, which most of us have been warned to avoid in order to minimize the risk of sunburn, premature aging, hyperpigmentation, and skin cancer. That’s why smart sun exposure (think daily morning walks vs. baking yourself at the beach) and supplementation are key to boosting your D levels. 

All that said, you should know that not everyone gets the same vitamin D benefits for their time soaking up the sun’s rays. A few different factors can impact your body’s ability to turn sunshine into the sunshine vitamin and to utilize the vitamin D you get through food or supplements. 

Why Is Vitamin D So Important, Again?

Technically a hormone, vitamin D has a hand in everything from supporting calcium absorption and bone growth, to modulating immune function, to regulating glucose metabolism, explains The Vitamin Shoppe nutritionist Rebekah Blakely, R.D.N. 

While vitamin D’s role in bone health isn’t new to most health-minded folks, its importance for a healthy immune system may have only first landed at the onset of the coronavirus pandemic, when people were searching for preventative measures. “Vitamin D helps activate T cells, or the ‘fighter’ cells of the immune system, which help identify and ward off infectious pathogens,” says Blakely. 

Another key benefit of vitamin D is that it has been shown to help regulate mood, per research published in the Indian Journal of Psychological Medicine. In fact, it’s often recommended that people who struggle during the winter months when the sun is scarce supplement with vitamin D.

You Probably Need More Vitamin D

Unfortunately, as many as 42 percent of Americans are not regularly getting enough vitamin D. The main culprit is likely a lack of sun exposure, according to research published in the medical journal Cureus. While certain foods—like mackerel, tuna, beef, cheese, eggs, and mushrooms—contain vitamin D, they only provide a small amount, making it difficult to reach the daily recommended amount (600 IU or 15 micrograms) through diet alone. 

Read More: 7 Groups Of People Who May Need More Vitamin D

Of course, this comes at a cost. Low vitamin D levels are associated with a higher risk of inflammatory conditions, infections, mood disorders, lowered immune function, weak bones, and more, according to Blakely. Some of the first signs of vitamin D deficiency may include low energy levels, mood changes, and muscle weakness.

Factors That Affect Your Ability To Absorb Vitamin D

Aside from not getting enough vitamin D through your diet or adequate sun exposure, what else could be standing in your way of achieving healthy levels? A few different things, potentially.

1. You have a darker complexion

Skin color surprisingly has a lot to do with how our body responds to vitamin D. In fact, research, including one recent PLOS Genetics study, has shown that individuals with a darker skin pigmentation are more susceptible to vitamin D deficiency due to the fact that they require longer periods of exposure to synthesize appropriate levels of the nutrient. This is likely one of the reasons why 82 percent of Black Americans and 69 percent of Hispanics are deficient in vitamin D, suggests research published in Nutrition Research.

2. You Religiously Apply SPF

While regular sunscreen use has been considered one of the best ways to protect your skin from the potentially harmful effects of the sun’s UV rays, it can unfortunately block out their biggest benefit: vitamin D.

Slathering on sunscreen all day every day basically sets you up for lower vitamin D levels, according to naturopathic doctor and clinical nutritionist David Friedman, N.D., D.C. “The body only requires 15 to 20 minutes of sunshine per day to get the vitamin D it requires—and skin doesn’t start burning until after 15 to 20 minutes of exposure,” he says. “You can safely expose yourself to the sun for 15 to 20 minutes—ideally not between the times of day when the sun is strongest, which is 10 a.m. to 3 p.m.—and then slather on the sunscreen for the rest of the day.”

3. You have high amounts of body fat

Research (like this one study published in The Journal of Nutrition) has long identified an association between high weight and low vitamin D levels. And more recent inquiries suggest that individuals with high levels of body fat have trouble meeting their recommended daily allowance of vitamin D.

You see, because vitamin D is stored in body fat, those with higher amounts of body fat may stash more of the nutrient away, leaving less in circulation for the body to use, Friedman explains. For this reason, people with overweight and obesity typically need much higher amounts of vitamin D to achieve the same serum volume as those of normal weight. 

4. You have digestive issues

Research has shown that individuals who suffer from digestive issues that lead to malabsorption of nutrients (including celiac disease, inflammatory bowel disease, and irritable bowel syndrome) can have trouble properly absorbing the vitamin D they consume through food. Often, it’s not the vitamin D itself that’s the issue, but the fact that many of these digestion-related diseases make it difficult to absorb fat, which is necessary for absorbing vitamin D, Blakely explains.

5. You take certain medications

Certain medications may also influence your vitamin D status. The most common medications that can contribute to vitamin D deficiency include steroids, laxatives, cholesterol medications, antifungals, antiretrovirals, and anti-seizure drugs, says Blakely. It’s also worth noting that certain natural supplements can have this effect, too. According to Friedman, several herbs can lower the body’s ability to absorb and utilize vitamin D, including kava kava and St. John’s wort.

What to do if you’re low on vitamin D

First thing’s first: Consider getting your vitamin D levels checked, even if you’re not experiencing any classic deficiency symptoms, since they don’t always show up, Blakely says. She recommends ensuring a level check is a part of your yearly physical.

If you’re low on vitamin D, aim to spend more time outside. “Expose as much of your skin as possible without sunscreen for 15 to 30 minutes,” Blakely says. She also recommends eating more fatty fish and whole eggs and drinking milk or juice that’s fortified with vitamin D.

Read More: The Best (And Worst) Time Of Day To Take Vitamin D

Additionally, discuss supplementation with your healthcare provider, who can calculate the daily amount you’ll need to take to correct any deficiency or insufficiency. “We typically aim to correct a deficiency within three months and then work out a maintenance dose,” says naturopathic doctor Rachel Corradetti-Sargeant, N.D. “Often, a maintenance dose sits around 2,000 IU per day; however, this can vary depending on the individual’s needs.” It’s not a one-size-fits-all situation, so working with a professional on an individualized plan is your best bet.