For many Americans (42 percent, to be exact), long winters and desk jobs are synonymous with vitamin D deficiency. Most of us spend little time directly exposed to the sun—and, depending where we live, struggle to get enough vitamin D from its distant rays when we do get outside.

Even without dark winters and indoor jobs, though, there are some people who need more vitamin D than others. Unfortunately, deficiency means greater risk of a whole slew of side effects that can affect health and well-being.

Why Vitamin D Is Crucial For Health

“Vitamin D—a.k.a. the ‘sunshine vitamin’—is one of the four fat-soluble vitamins (the others are vitamins A, E, and K),” says Charlotte Martin, M.S., R.D.N., C.P.T., dietitian and owner of Shaped by Charlotte. Why the nickname? The body produces vitamin D from cholesterol when exposed to the sun’s rays.

Thing is, vitamin D is unique because it actually acts more like a hormone than a vitamin. 

“Vitamin D is needed for a variety of functions in the body, like cholesterol production, healthy immune system function, and calcium absorption, which promotes strong bones,” says Maggie Michalczyk, R.D.N., Chicago-based dietitian and blogger behind Once Upon a Pumpkin.

Read More: Science Offers More Reasons To Take A Daily Multivitamin

According to Martin, vitamin D is also linked to reduced risk of heart disease and some cancers, as well as mood regulation and mental health. In fact, ample amounts of vitamin D may be associated with increased levels of serotonin and melatonin, according to a 2017 study out of the U.S. Army Institute of Surgical Research. (Low levels of these two hormones are linked to Seasonal Affective Disorder, or SAD.)

Though the official daily recommended intake for vitamin D is 600 IU (or 15 micrograms), many experts believe most people can benefit from more, says Michalczyk. How much more is still up for debate.

Signs Of Vitamin D Deficiency

“The signs and symptoms of a vitamin D deficiency include constant fatigue, getting sick often, depression, slow wound-healing, bone pain and/or loss, and hair loss,” says Michalczyk.

To identify low vitamin D—or a true deficiency—a doctor can perform a blood test. (Vitamin D checks are typically part of yearly physicals.)

People Who Need More Vitamin D

Though many people face risk of low vitamin D levels these days, certain groups should pay especially close attention to their D status.

1. Those With Limited Sun Exposure 

“Since our body produces vitamin D with the help of sunlight exposure, our levels can be affected when we don’t get enough sun,” says Michalczyk.

If you don’t spend at least 10 to 30 minutes in the sun a few times per week (or more), you likely don’t get enough exposure to support healthy vitamin D levels. Yep, that means most people who work desk jobs or wear SPF when they do get outside likely miss out on D.

2. African American And Hispanic People

“Individuals with darker skin have more melanin (the pigment that gives skin its tone) in the outermost layer of their skin, which doesn’t absorb as much UV radiation,” says Martin. As a result, they may have a more difficult time producing ample vitamin D from sun exposure alone.

3. People With Higher Body Fat Percentages

Although the exact mechanism at play here remains unclear, those with higher levels of total and abdominal fat are more likely to have lower vitamin D levels, says Martin. Check in with your physician to learn more about whether your body fat percentage may be influencing your vitamin D needs.

4. People On Strict Vegan Diets

“Since foods like cheese and egg yolks are good sources of vitamin D, excluding them from your diet can lead to a vitamin D deficiency,” says Michalczyk.

Read More: 7 Tips For Doing A Plant-Based Diet Right

In fact, many forms of dairy- and fish-limiting diets (including veganism and some forms of vegetarianism) are associated with higher rates of deficiency, adds Jonathan Valdez, R.D., owner of Genki Nutrition and spokesperson for New York State Academy of Nutrition and Dietetics.

5. The Elderly

“Since vitamin D needs to be activated by the kidneys, age-related declines in renal function can contribute to lower vitamin D status in the elderly,” says Michalczyk. Not to mention, just as renal function declines, so does our ability to synthesize vitamin D from sunlight.

For these reasons, “the recommended dietary allowance for vitamin D for those over 70 years of age increases up to 800 IUs,” says Martin.

6. Breastfed Infants

Believe it or not, “human milk actually does not provide adequate amounts of vitamin D,” says Valdez. (Plus, many moms have low D to begin with.) Given that, partially and exclusively breastfed infants often need liquid vitamin D supplements of around 400 IU per day.

7. People With Kidney Issues

People with CKD (chronic kidney disease) are another group prone to vitamin D deficiency because their kidneys have a hard time converting vitamin D into its active form, says Valdez. In fact, people with kidney issues typically need more and more assistance from supplements as their condition progresses.

How To Add More Vitamin D To Your Diet

Ideally, we’d all spend enough time outside to get the vitamin D we need from the sun.

According to the National Institutes of Health, five to 30 minutes of sun exposure between 10 in the morning and 3 in the afternoon at least twice a week should support sufficient vitamin D synthesis. The key: to forego sunscreen and expose your face, arms, legs, and/or back. (The more skin, the better.)

Unfortunately, few foods are naturally good sources of vitamin D. Your options include:

• fatty fish (salmon, tuna, mackerel)
• fish liver oils
• beef liver
• cheese
• egg yolks

For reference, cod liver oil provides a whopping 1,360 IU of vitamin D, while salmon offers 447 IU and an egg contains just 41 IU.

Since many Americans don’t eat fish (or organ meats) regularly, most get vitamin D from fortified foods, such as milk, breakfast cereals, orange juice, yogurt, and plant-based milks. (OJ typically contains the most, with many brands coming in around 137 IU.)

Supplementing With Vitamin D

Vitamin D supplements can also be hugely helpful for people who need to increase their D levels, says Martin. You’ll typically find supplements in the form of vitamin D3 (cholecalciferol). 

Since your vitamin D needs depend on your current levels, age, sex, and whether or not you’re pregnant or breastfeeding, consult with your doctor or a dietitian about how much to supplement with. Yale Medicine recommends starting out with a supplement that offers the daily recommended allowance for your age.

For most healthy people, it’s 600 IU per day, but for people over age 70, it’s about 800 IU. Babies should be getting smaller amounts in their first year of life (between 200 and 400 IU), according to Yale. 

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