“The sunshine vitamin” is a very fitting name for vitamin D. While the sun itself isn’t giving off vitamin D as it shines, our bodies absorb its UV rays, and they react with other compounds in our skin to convert them to this essential vitamin.
We need vitamin D for many things—the most important of which is bone health. Our bodies are able to make as much as we need, but only if we get adequate sun exposure. Since most of us work indoors all day, we’ve turned ourselves into a pretty D-deficient society. In fact, about one-third of U.S. adults are deficient. “Before industrial times, when people were essentially outdoors a lot, vitamin D levels were much higher than today,” Edward Giovannucci, M.D.
To add fuel to the fire, when we do spend time outside, we’re more conscious about dutifully slathering on SPF (great news on the cancer-prevention front, but not great for D levels), Zhaoping Li, M.D., Ph.D., professor of medicine and chief of the division of clinical nutrition at UCLA, tells SELF. “With all those measures, we’re really decreasing our skin’s capability or chance to make vitamin D.” And over time, this nutrient deficiency can cause some pretty significant health effects.
Why do we need vitamin D?
- Bone Health: Vitamin D’s primary job is to maintain bone health. “It makes our body capable of absorbing calcium,” Li explains. In our intestines, there’s a specific type of transporter responsible for moving calcium from our food into the blood, so our bones and organs can use it. “The number of transporters in the bowel is reliant on vitamin D—it’s the key regulator for how many are available and how functional they are,” Li explains. Without enough D, we can’t absorb calcium from our food, which can be very damaging to our bones over time. Vitamin D also regulates levels of calcium and phosphorous—another important mineral for healthy bones—in the blood.’
- Cell Growth: “Vitamin D also plays an important role in overall cell growth, particularly in how they divide and multiply,” Li says. “There has also been some evidence showing if you don’t have enough, you may have an increased chance of colon cancer.”
- Immune Function: Vitamin D is also connected to immune function. “People who are vitamin D deficient may have sub-optimal immune systems that make them prone to some infections, such as tuberculosis, some auto-immune disease such as multiple sclerosis, and possibly some cancers,” Giovannucci says. Research suggests compromised immune function due to lack of vitamin D may also influence the development of allergies and asthma.
How can you tell if you’re deficient?
You’re officially considered D-deficient if your levels are below 20 ng/mL (nanograms/milliliter). “By this standard, about one-third [of U.S. adults] are deficient,” Giovannucci says. “But it varies by ethnic group: About 25 percent of whites, 50 percent of Mexican-Americans and 80 percent of African-Americans [are deficient].” Obese people are also more prone to vitamin D deficiency. Some experts believe, though, that 30 ng/mL should be the standard. “If this is used, deficiency rates would be much higher.”
- Blood Test: The only way to know your vitamin D levels is through a blood test. Until a few years ago, this wasn’t part of a routine physical exam, but now doctors test for it regularly, Li says. “People just never bothered to check, and we spent a lot more time outdoors in the past, which is part of the reason.”
- Bone Pain: When levels dip extremely low, to less than 10 ng/ml, some people may experience bone pain, Giovannucci notes.
But for most otherwise-healthy adults who are slightly deficient, it’s likely there won’t be any signs. “It’s very common not to have symptoms, especially for mild deficiency.” Studies have suggested that symptoms like tiredness, weakness, and sadness or depression can signify low vitamin D levels, but experts are skeptical. “There may be some people that experience symptoms such as tiredness with very low levels, but this isn’t proven,” Giovannucci says. Same thing with being in a crummy mood. He actually suggests the depression connection might work in the opposite way. “What happens sometimes is that people who don’t feel well don’t go outdoors, so they may get little sun exposure. Thus, it may be that feeling blue may indirectly lead to lower vitamin D.”
After you’ve been very deficient in vitamin D for a long period of time, you may start to lose bone density and develop conditions like osteopenia and osteoporosis, because your body hasn’t been able to use calcium correctly. This is especially a concern for women, because hormonal changes that come with menopause already increase the risk and rate of bone loss. Li notes that taking a calcium supplement isn’t sufficient because “you need D to transport it,” and taking too much calcium without exercising enough may cause it to go to other parts of the body, like the arteries, instead of bones, increasing your risk for heart disease and heart attack. “So now people are really backing down on calcium supplementation. Instead, they’re giving more vitamin D and allowing the body to do its job and regulate how much calcium it needs.”
What can you do to get more D?
- Get More Sun: The easiest way to get more vitamin D is to get more sun. But it’s tricky, balancing heathy sun exposure with too much. “I wouldn’t recommend excessive sun exposure to maintain vitamin D, certainly not burning,” Giovannucci says. “On the other hand, we shouldn’t feel paranoid about any sun exposure.”
For a very light-skinned person exposed to midday summer sun, 10 minutes of sun exposure can be enough for the day. But the amount of skin you have exposed, the season and time of day you’re outside, and your skin color—people with darker skintones actually need more sun exposure to make the same amount of vitamin D as those with lighter skintones do—all influence how much sun you’ll need specifically to reach optimal D levels.
- From Your Diet: In addition to getting more sun, you can get some vitamin D from your diet (though usually not quite enough). The best source? Mushrooms. “Mushrooms have a system very similar to our skin,” where they can use sunlight to make vitamin D, Li explains. Leafy greens and liver (which you’re probably not eating on the reg, or like, ever) also naturally have some D in them. Most dairy products, breakfast cereals, and orange juice are now fortified, which means vitamin D is added to them. But realistically, you’re probably not eating enough D-rich foods every single day.
- Taking A Supplement: Giovannucci says taking a supplement of at least 1,000 or even 2,000 IU per day is usually the most practical way for people to maintain vitamin D levels, but your doc may prescribe more or less depending on how deficient you are. Most doctors will recommend taking vitamin D3 (cholecalciferol) supplements specifically. Li notes that if you have super low levels and are at high risk for bone loss, your doctor may recommend up to 5,000 IU per day, or even vitamin D injections. If you ever have any bone pain, see your doctor to find out whether your lack of D (or something else) may be to blame. If you keep tabs on your levels and talk with your doctor to find the best plan of attack for you, you can safely and efficiently avoid deficiency and let your body reap the benefits of adequate vitamin D.