When winter hits, the temperature isn’t the only thing that drops: Your vitamin D levels can drop too. If you’re anything like most of the US population, you can’t really afford the dip either: Estimates of how many people are low on vitamin D vary, but it seems like many of us could use more. Data from the 2011 to 2014 National Health and Nutrition Examination Survey shows that insufficient or deficient levels are relatively common, peaking among adults ages 20 to 39. Worse, those percentages rise during the cold months, as a 2002 study published in The American Journal of Medicine shows.
Vitamin D is a key nutrient that we can get from our diets or make for ourselves with the help of sun exposure. Not having enough can be an issue, since it does a lot for our bodies. While vitamin D might be best known for working in tandem with calcium to help you build and maintain strong bones, it’s important for many other aspects of our health, playing vital roles throughout the body, much like a hormone does. As SELF has reported, research suggests that sufficient vitamin D may help protect you from respiratory infections, promote healthy blood sugar levels, prevent pregnancy complications, and perhaps even reduce your risk of developing or dying from various types of cancer.
So how do you get more vitamin D? And how do you suss out if you need more in the first place? Here’s what you should know.
How to know if you need more vitamin D
Vitamin D deficiency happens when you don’t have enough of the nutrient circulating in your blood. Your doctor can spot vitamin D deficiency through a simple blood test, with results reported in either nanomoles per liter (nmol/L) or nanograms per milliliter (ng/mL), according to the Office of Dietary Supplements (ODS) at the National Institutes of Health. Normal levels—the amount considered adequate for both general and bone health for most people—are greater than 50 nmol/L (20 ng/mL). Levels from 30 to 50 nmol/L (12 to 20 ng/mL) are low and considered inadequate for general and bone health at large. Once they drop below 30 nmol/L (12 ng/mL), that’s considered a deficiency.
While low or deficient vitamin D levels are associated with a variety of health issues, like heart disease, diabetes, and depression, there isn’t definitive evidence showing that lack of vitamin D is necessarily the cause of these issues—or that getting more vitamin D can help prevent them. However, the ODS says vitamin D deficiency has been found to lead directly to osteomalacia, a condition that softens bones and can cause symptoms like bone pain, muscle weakness, and muscle spasms. Vitamin D deficiency can also contribute to the bone disease osteoporosis, which drastically raises the risk of bone breaks, especially in older women.
Feeling fatigued and weak are other potential signs of deficiency, Shana Minei Spence, MS, CDN, a registered dietitian nutritionist based in New York City, tells SELF. That said, these symptoms aren’t necessarily a reliable indicator, since they can be caused by a variety of health issues. Besides, many people with a deficiency have no noticeable symptoms at all.
That’s why the only way to be sure is with a blood test and an official diagnosis from a doctor. Some doctors order these tests routinely; others don’t, Sue Shapses, PhD, RD, a professor of nutritional sciences at Rutgers University, tells SELF. “Should people ask for their levels? I would say that, if you think you’re at risk, yes,” she says.
While anyone can experience low or deficient vitamin D, there are some risk factors that can make it more likely. According to an analysis of 2011 to 2012 National Health and Nutrition Examination Survey data published in Cureus in 2018, these risk factors include:
- Darker skin color. Sunlight stimulates your skin to produce its own vitamin D for your body. People with darker skin make less vitamin D in the sun than people with lighter skin because the melanin, or pigment, scatters the UV rays that are key to this process.
- Low dairy product consumption. Most milk sold in the US is fortified with vitamin D, so milk drinkers may have a lower risk of deficiency than people who don’t consume dairy daily, like those who eat a vegan diet or are lactose intolerant.
- Smoking. Cigarette smoke may impair the expression of a gene that helps your body utilize circulating vitamin D. (Add this to the long list of reasons not to smoke!)
- Certain malabsorption conditions. Some people become deficient in vitamin D not because they don’t consume enough of it, but because they have a condition that inhibits fat absorption (like Crohn’s disease or celiac disease), and vitamin D is a fat-soluble nutrient. People who have undergone gastric bypass surgery may be at risk too, since that procedure can also reduce the absorption of fat-soluble vitamins.
Now that we’ve established why vitamin D is important and how you can benefit from a boost, it’s time to explore your options for doing so. There are three basic ways to get vitamin D into your body: sunlight, food, and supplements. Here’s what to know about each.
1. Sunlight
Your skin starts manufacturing vitamin D when exposed to the sun’s UV rays, Dr. Shapses explains. Most people meet some of their vitamin D requirements this way, per the ODS, and people who spend a lot of their time inside may be more prone to deficiency, Spence says. However, there are some variables at play that make things more complicated. “I think people rely on the sun because of the term sunshine vitamin,” Spence says, but the sun may be a less dependable source of vitamin D than you think.
For starters, there aren’t any official guidelines for sun exposure and vitamin D. Some evidence suggests that 5 to 30 minutes of sun exposure a day (or at least twice weekly) is adequate for your skin to produce enough of it, according to the ODS. But the amount of sunshine any one individual needs to make an adequate amount of vitamin D really depends on a bunch of different factors, including your location, the season, smog levels, skin coverage exposure, sunscreen use, cloudiness, age, and skin color, the ODS explains.
Season-wise, for instance, winter is typically a time to be more concerned about low vitamin D levels since your sun exposure is reduced, Dr. Shapses says. For the same reason, geography matters too: Generally speaking, the farther you live from the equator, the less sun you get year-round, Spence says. One 2010 study published in the Journal of the American Academy of Dermatology found that a person with a medium skin tone could produce 400 international units (IU) of vitamin D by spending three to eight minutes in the sun at noon in Boston between April and October. In contrast, they could make the same amount in three to six minutes in Miami no matter the month.
Skin color is another consideration. Again, people with naturally darker skin produce less vitamin D because melanin scatters UV rays. Primarily because of this, Black people are more likely to have lower vitamin D levels—by nearly double, according to some estimates. (That said, it’s not totally clear whether this negatively impacts their health, the ODS explains, as folks of African ancestry also have lower rates of bone fracture and osteoporosis than white people do.) Either way, the advice around sun exposure for vitamin D production is the same for all people regardless of skin color.
That said, we also know that sun exposure comes with a cost: It increases our risk of skin cancer, the most common cancer in the US. That’s why sunscreen is a must when you go outside. And in case you were concerned, it shouldn’t interfere with your body’s ability to synthesize vitamin D: People typically don’t put enough sunscreen on exposed areas to totally shield their skin from the vitamin-D-producing rays in sunlight, according to the ODS. So by all means, enjoy your time in the ’shine—but keep slathering on that SPF (minimum SPF 30). And instead of depending solely on the sun, look to your diet to help you hit your vitamin D goals. (Keep reading for tips on how to do that.)
2. Food
While your body makes some vitamin D from sunlight, you’ll need the nutrient in your diet too, Spence says. The recommended daily allowance (RDA) for vitamin D—which is calculated on the assumption that people are getting minimal sun exposure—is 600 IU of vitamin D per day for everyone from the ages of 1 to 70, according to the ODS. (We’ll give a few examples below to help you gauge what that amount actually looks like.)
The thing is, vitamin D doesn’t occur naturally in very many foods, according to the ODS; the best natural sources are fatty fish like trout, salmon, tuna, and mackerel. (Yet another reason to eat the two servings of fatty fish per week recommended for heart health, Dr. Shapses says.) For example, cooked pink salmon has 647 IU of vitamin D per half fillet, according to the USDA.
Some other animal products, like cheese, egg yolks, and fatty meats, also have small amounts of vitamin D. For example, you can find 88 IU of vitamin D in a three-ounce serving of braised pork spareribs and 44 IU in a large hard-boiled egg, according to the USDA.
On the other end of the food spectrum, certain mushroom varieties are also a good source of vitamin D (PSA to vegans, vegetarians, and those who prefer plant-based items!), and are sometimes even treated with UV light to produce extra, according to the ODS. Per the USDA, morel, chanterelle, maitake, and UV-treated portabella mushrooms tend to contain the most vitamin D, although levels vary based on growing and storage conditions. For instance, chanterelle mushrooms have about 114 IU per cup.
Most of the vitamin D in the American diet, however, comes from foods that are fortified with vitamin D. Nearly all dairy milk sold in the US falls into this category, according to the ODS. (You can get 117 IU per cup of 1% milk with added vitamin D, for example.) Yogurt, plant-based milks (like soy, almond, or oat milk), cereal, and orange juice are also commonly fortified. For example, Cheerios have 60 IU of vitamin D in each 1.5-cup serving. Whatever your preference, adding in more foods that are naturally rich in vitamin D or fortified with it can help increase your intake.
3. Supplements
It’s possible to get enough vitamin D in your diet, but it’s not always easy. “If people aren’t eating a variety of foods, especially cereals, milks, yogurt, and fish, then a supplement might be needed,” Spence says.
Just a few disclaimers: It’s always smart to check with your doctor before starting a new supplement, and to do your homework before buying. If a blood test reveals a deficiency, your doctor can give you a prescription supplement or recommend an over-the-counter supplement in a dose that can restore your levels to normal, Dr. Shapses says. If you work with a registered dietitian, they may also recommend a supplement, Spence says, as well as counsel you on dietary sources of vitamin D.
The vitamin D found in supplements comes in two main forms: D2, or ergocalciferol (the plant form) and D3, or cholecalciferol (the animal form). Most doctors recommend vitamin D3 because it is slightly more active in the body and, in turn, slightly more potent, according to Columbia University Irving Medical Center, but both forms are effective at correcting a deficiency. In general, doses of 600 IU to 1,000 IU of vitamin D per day are pretty safe, Dr. Shapses says. (Many multivitamins contain about 1,000 IU of vitamin D, she notes.) Spence typically recommends 600 IU for women up to age 70 from a brand that is USP-verified. (This certification means the product contains the ingredients listed on the label in the declared potency and amounts, does not contain harmful levels of specified contaminants, will break down and release into the body within a specified amount of time, and has been made according to the US Food and Drug Administration’s Good Manufacturing Practices, according to USP. But keep in mind that the FDA itself doesn’t regulate supplements in general.)
You should only take higher doses (5,000 IU to 10,000 IU per day) if specifically recommended by your doctor, Dr. Shapses says. If your doctor diagnoses you with a vitamin D deficiency, they may prescribe a special high-dose supplement for you to take for a short time, about 8 to 10 weeks. This can bring your levels up—back into the normal zone—fast.
Following your doctor’s orders is especially important in this case because there is a risk of excessive vitamin D supplementation due to mistakes in the manufacturing process or simple user error (say, taking significantly more than directed). Whatever the cause, this can result in extremely high levels of vitamin D (greater than 125 nmol/L or 50 ng/mL), which can lead to adverse health effects like nausea, vomiting, muscle weakness, and kidney stones, the ODS says.
If you’ve been diagnosed with low or deficient vitamin D or simply want a boost, talk to your health care provider about the various ways to increase the levels of vitamin D in your body—whether through spending more time in the sun, making different food choices, or taking a daily pill. And if you want to know whether your efforts are paying off, there’s only one way to find out: That’s right, you’re going to need to get that blood test.
Related:
- B12 Supplements and IVs Promise an Energy Boost. Here’s What the Science Says
- 5 Subtle Signs of Seasonal Depression to Watch Out For
- How to Prep Now If Winter Always Makes You Depressed
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