One reason your body needs vitamin D is to support bone health. Vitamin D helps your intestinal tract and kidney absorb calcium, so your body has more available to build healthy bones and keep your skeleton strong and mobile. There’s also evidence that vitamin D matters for a healthy immune system, too. In fact, many immune cells have receptors for vitamin D on their surface.
Are there other health benefits of Vitamin D? Whether getting more of the sunshine vitamin lowers the risk of health problems is still not clear, although there is some evidence that maintaining a healthy level of vitamin D may be beneficial for people with autoimmune disorders.
Some studies also suggest that having a healthy vitamin D level may reduce the risk of catching some respiratory infections. In fact, vitamin D regulates over 200 genes in the human body. Despite the importance that vitamin D plays in health, studies show over a billion people worldwide are deficient or have sub-optimal levels of this vitamin, partially because of lifestyle changes that require people to spend time indoors.
How Your Body Gets Vitamin D
The way most people meet their body’s vitamin D requirements is through sun exposure. When sunlight hits your skin, dehydrocholesterol on the surface of your skin forms pro-vitamin D3. This goes on to be activated to full vitamin D3 by the liver and kidneys. Sunlight is made up of three types of ultraviolet rays, UV-A, UV-B, and UV-C. It’s UV-B rays that trigger vitamin D3 synthesis. If you block UV-B rays, your skin can’t form vitamin D3.
You might wonder whether your skin can still make vitamin D3 if you wear a sunscreen that blocks ultraviolet rays from the sun. With the rise in cases of skin cancer and malignant melanoma, more dermatologists recommend wearing sunscreen when outdoors. However, your skin’s ability to make vitamin D3 will be impeded if all of your exposed skin is covered by sunscreen. Most sunscreens are broad-spectrum sunscreens and block both UV-A and UV-B rays and all sunscreens reduce UV-B. So, you can’t count on sun exposure while wearing a sunscreen to raise your vitamin D level. Yet as Harvard Health points out, the amount of sunscreen people apply is often insufficient to block all UV-B rays, so you still get some vitamin D production unless you apply a heavy layer of sunscreen.
To meet your body’s vitamin D needs through sun exposure, you need to expose at least 40% of your skin to 15 minutes of sunlight daily. That’s not practical for most people, so it’s not surprising that deficiency is so common. And as you can see, wearing a sunscreen or sunblock reduces your skin’s ability to produce vitamin D but may not completely block it. You’re getting less vitamin D, but still getting some. Most windows, including car windows, also block UV-B rays, so sitting behind glass with the sun shining through isn’t a reliable way to boost your vitamin D level.
Food Isn’t a Good Source of Vitamin D Either
What about diet? Most food is not a good source of vitamin D, although some contain modest amounts. For example, oily fish, like salmon, liver, and egg yolks contain moderate quantities of vitamin D3. Some foods, like boxed cereals, yogurt, orange juice, and dairy products, are fortified with vitamin D, although the form in these products is usually vitamin D2. However, some studies suggest that vitamin D2 isn’t as efficient at raising levels of the active hormone. If you expose mushrooms to sunlight, they also form vitamin D2. Therefore, ideally, you want your vitamin D sources to be foods that contain vitamin D3 or sunlight.
Can You Get Enough Sun Exposure to Maintain a Healthy Vitamin D Level?
Whether you can get enough vitamin D from sunlight depends on how much time you spend outdoors, the time of year, and where you live. At certain latitudes, like around Boston, there’s not enough sunlight to trigger vitamin D production from November to early spring. So, it’s not surprising that many people in the Northern parts of the United States are vitamin D deficient.
Plus, skin color, age, and body weight affect vitamin D status. People who have darker skin tones need more sun exposure to make enough vitamin D relative to those with light skin. The skin pigment melanin deflects some of the UV-B rays that you need to make vitamin D3. Being older and having more body fat also makes it harder to maintain a healthy vitamin D level.
The Bottom Line
There are reasons to wear sunscreen, especially if you’re at high risk of skin cancer. However, sun exposure while wearing sunscreen will reduce the amount of vitamin D your body can make. If you wear sunscreen every day, taking a vitamin D supplement might be appropriate since you can’t count on food to provide enough of the “sunshine” vitamin.
The best way to find out how much to take is to check a vitamin D level and discuss the results with your physician. They can recommend an appropriate dose based on your level. If you don’t know your level, it’s safest not to supplement with more than 1,000 to 2,000 I.U. per day. Your liver stores excess vitamin D and it is possible to accumulate too much.
If you take a vitamin D supplement, buy it from a reputable supplier and choose the vitamin D3 form since it is the most efficient at raising your body’s vitamin D level. Be sure to follow your vitamin D level if you take over 1,000 to 2,000 I.U. per day. It’s rare, but people who take a high-dose supplement for a long period of time can develop vitamin D toxicity. However, you won’t develop toxicity from getting vitamin D from sunlight or foods since your body can self-regulate vitamin D from these sources.
- The Center for Evidence-Based Medicine. “Vitamin D: A rapid review of the evidence for treatment or prevention in COVID-19”
- com. “Vitamin D2 vs. D3: What’s the Difference?”
- Am J Clin Nutr. 2012 Jun;95(6):1357-64. doi: 10.3945/ajcn.111.031070. Epub 2012 May 2.
- Harvard Health Publishing. “On call: Vitamin D2 or D3?”
- Medscape Family Medicine. “Vitamin D: A Rapid Review”
- Am J Clin Nutr. 2008 Apr;87(4):1080S-6S. doi: 10.1093/ajcn/87.4.1080S.
- org. “What is vitamin D toxicity? Should I be worried about taking supplements?”
- 2013 Jul; 5(7): 2502–2521.Published online 2013 Jul 5. doi: 10.3390/nu5072502.
- Harvard Health Publishing. “6 things you should know about vitamin D”