A large portion of the vitamin D our bodies absorb is derived from the sun, so it makes sense why many people assume that supplementing with vitamin D is only necessary in the winter, when the days are shorter and clouds are abundant. But is it really wise to stash away your vitamin D supplement as soon as your floats, boats, and swimsuits come out of storage?
Ahead, learn exactly how the body converts sunlight into the sunshine vitamin and why your levels may still be low in a season of clear skies. We’ll also break down why adequate vitamin D levels are so important, the symptoms of low vitamin D, and the proper protocol for supplementation.
- ABOUT OUR EXPERTS: Karen Linardakis-Cooney B.C.H.H.P., C.N., is a board-certified holistic health practitioner and a nutritionist with The Vitamin Shoppe. Brittany Michels, R.D.N., M.S., C.P.T., is a registered dietitian and certified personal trainer with The Vitamin Shoppe.
How The Body Absorbs Vitamin D From The Sun
The body synthesizes vitamin D when the sun’s ultraviolet B-rays penetrate the outer layer of skin (the epidermis), explains board-certified holistic health practitioner Karen Linardakis-Cooney B.C.H.H.P., C.N., a nutritionist with The Vitamin Shoppe. From there, the body transforms a naturally occurring form of cholesterol (7-dehydrocholesterol) into a usable form of vitamin D (vitamin D3) with the assistance of a handful of helper enzymes in the skin.
In optimal conditions, just five to 30 minutes of sun exposure each day is sufficient for maintaining healthy vitamin D levels, per the American Journal of Lifestyle Medicine. However, assuming your D levels remain on autopilot all summer long can be problematic. For starters, even throughout the summer, many people don’t spend enough time outside to support healthy vitamin D levels. One survey of 5,000 adults found that nearly 40 percent of Americans get less than 30 minutes of outdoor time each day, while close to 20 percent spend less than 15 minutes outside per day.
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Second, some populations aren’t able to produce as much vitamin D, even with sun exposure. For example, “people with darker skin tend to have lower blood levels of vitamin D because the pigment (melanin) acts like a shade, reducing production of vitamin D when the sun hits the skin,” says Cooney. Meanwhile, older folks may struggle to convert sun rays to vitamin D as cholesterol levels decrease as we get older. “Studies have also found that obese individuals are at higher risk of vitamin D deficiency,” says Brittany Michels, R.D.N., M.S., C.P.T., a registered dietitian and certified personal trainer with The Vitamin Shoppe. One study published in the journal Medicina, suggests that this is because the nutrient gets diluted by the volume of fat. Even if they hit the mark on daily outside time, these populations might fall short on the sunshine vitamin.
When Being Outside Isn’t Enough
It’s also important to note that not all time outside is created equal—at least when it comes to vitamin D production.
“Production of vitamin D in the skin from sunshine is significantly reduced or completely muted when we wear sunscreen,” says Michels. Ditto goes for wearing sun-protective clothing. The only way to trigger the chemical reaction that turns cholesterol into vitamin D3 is for sunlight to hit your skin directly, she says. In fact, you need to expose a significant amount of your body for that five to 30 minutes of sunshine to ladder up to adequate vitamin D.
You see, vitamin D production requires direct UVB exposure, which means habitually lying under an umbrella, wearing long sleeves and pants, and otherwise avoiding the full impact of the sun all result in low levels of vitamin D, says Michels. Case in point: One 2019 study published in the International Journal of Endocrinology found that women who wore hijabs, veils, and other clothing to cover their whole bodies for religious and/or cultural reasons faced a heightened risk for vitamin D deficiency, due to the lack of direct sunlight exposure. Meanwhile, research published in Nutrition Research reported that individuals who wore clothing with more coverage had a higher risk of deficiency than those who wore less clothing and left more skin bare.
Read More: 5 Possible Reasons Why You’re Not Absorbing Enough Vitamin D
The thing is, excess exposure to UVB rays can cause sunburn, damage the DNA in skin cells, and contribute to most types of skin cancer, according to the American Cancer Society. So the solution isn’t necessary to forgo sun protection altogether. “The question is how to balance your vitamin D needs with your desire to protect yourself from sun damage—and there isn’t a perfect answer,” says Cooney.
For people with risk factors for skin cancer—such as lighter skin, eyes, and hair, and a personal or familial history of skin cancer—that might mean choosing to be very cautious about sun exposure, she suggests. Others, however, may choose to prioritize spending five to 30 minutes outside with at least 40 percent of their skin exposed in the name of adequate vitamin D levels, adds Michels.
Clearly, there are a few reasons you might need some extra support in the vitamin D department throughout the summertime.
Vitamin D Is Very Important to Your Health
Many people off-handedly blame the lack of sunlight and vitamin D on their despair and despondency, grumps and grumbles, snaps and sads. And it’s for good reason: Vitamin D is an antioxidant, and has been shown to have a powerful impact on mood.
However, this nutrient does far more than support your mood. “Vitamin D supports mitochondria, which are the energy producers of our cells,” says Michels. It also helps with maintaining healthy levels of testosterone, a hormone that regulates muscle and fat mass, sex drive, and fertility, she adds. So, inadequate intake can lead to body composition changes as well as low libido.
Vitamin D also regulates the function of over 200 genes in the body, which means adequate circulating levels are necessary for their expression, Michels explains. Per research published in Nutrients, the genes modulated by vitamin D include those connected with calcium and phosphorus levels and immunity.
Given D’s role in supporting calcium and phosphorus levels on the gene level, it can also be considered essential in bone health and muscle function, Cooney notes. “We need calcium and phosphorus for strong bones and teeth, and they also help our muscles contract, carry messages between the brain and the body, and keep our cells functioning well,” she says.
Vitamin D Needs and Symptoms of Deficiency
Whether you’re male or female, lactating or pregnant, the vitamin D Recommended Dietary Allowances (RDAs) say that everyone between the ages of 19 and 70 needs at least 600 IU of Vitamin D per day. However, given vitamin D’s importance plus limitations in our understanding of how much vitamin D actually absorbs into the system, other nutritional bodies recommend even more per day. The Endocrine Society, for example, suggests that adults might need up to 1,500 to 2,000 IU per day for optimal health.
When individuals do not get enough vitamin D and become deficient, they risk symptoms such as fatigue, poor sleep, bone pain, depression, hair loss, muscle weakness, loss of appetite, and increased incidence of sickness, per Cooney. Vitamin D deficiency has also been linked with depression, anxiety, and changes in metabolism.
Rather than waiting around to see if deficiency symptoms hit you, Michels recommends getting your vitamin D levels checked with a blood test. Yes, even if it’s mid-summer and you live in a sunny state like Florida, California, Texas, or Hawaii. “You should always be proactive about knowing your vitamin D levels,” she says.
How To Get Enough Vitamin D All Year Long
Outside of sunshine, you can increase your vitamin D intake through food and supplements.
Few foods naturally contain vitamin D, and most that do—cod liver oil, salmon, swordfish, tuna fish, sardines, beef liver, and egg yolks—aren’t part of most individuals’ daily intake, says Cooney. There are some foods and drinks, however, that are fortified with vitamin D. Primarily, these include dairy milk, plant-based milk alternatives, orange juice, and cereals, she says.
Even with fortification, though, it is hard to consume enough vitamin D through food, Cooney says. That’s why taking a supplement is often vital—even in the summer.
Picking a Vitamin D Supplement
Vitamin D supplements contain two main forms of vitamin D: D2 (ergocalciferol) and D3 (cholecalciferol). “Vitamin D2 is produced by plants exposed to sunshine, while vitamin D3 is the type in animal products, as well as the kind produced when human skin is exposed to sunlight,” says Michels. Research suggests that D3 is more effective at raising vitamin D blood levels than vitamin D2, and therefore is the type Michels recommends individuals look out for. (For the record: There are vegan vitamin D3 supplements available).
Most vitamin D3 supplements offer a dose ranging from 1,000 to 5,000 IU, but just how much you need will ultimately depend on your reported starting levels, according to that blood test. “Vitamin D3 supplements come in softgels, capsules, tablets, drops, sprays, chews, gummies,” says Michels. She suggests opting for whatever form will be easiest for you to add to your routine.
When taking your supplement, Michels suggests doing so with food—and, ideally, healthy fats. Vitamin D3 is a fat-soluble nutrient, she explains, which means it is best absorbed when fat is present. Some vitamin D supplements include a fat source (typically an oil), but whether or not you need a fat-containing option depends on when you supplement. “If you consume your vitamin D in the middle of the day without food, it may be beneficial to have a fat source included in your supplement,” Michels says. “But if you consume vitamin D with a fat-containing meal every day, then you may not need a fat source included.”
The Bottom Line
Vitamin D deficiency is possible all year round, including in the warm and sunny months. Given that inadequate levels can lead to a variety of unfavorable symptoms, it’s in the service of your overall health and well-being to get your levels checked and continue supplementation through the summer, if necessary.