How convenient it is to get one of your daily vitamins from the sun. While other vitamins are typically obtained through dietary sources, vitamin D—also known as the “sunshine vitamin”—can easily be obtained by simply soaking up those rays.
“Vitamin D is important for healthy bones, along with other nutrients such as calcium, magnesium and vitamin K,” says Erin Stokes, N.D. “In addition, vitamin D supports healthy immune function, which is top of mind during the winter months. Maintaining optimal levels of vitamin D can also contribute to an overall sense of well-being.”
However, in practice, we know that getting enough of that sunshine vitamin is far more complicated than it seems. Environmental factors, seasons, conditions (such as skin cancer risk), and even your location play a big part in how much vitamin D you actually get during the day. So how does one know if they are getting enough vitamin D, and when would it be wise to take a vitamin D supplement?
Factors That Affect Vitamin D Levels
According to the National Institutes of Health, vitamin D is a fat-soluble vitamin that promotes calcium absorption in the gut and helps you maintain healthy, strong bones. Getting a sufficient amount of vitamin D can also help to reduce inflammation in the body.
However, an estimated 22% of people in the United States have moderate vitamin D deficiency, per a 2022 article in Frontiers in Nutrition. What’s more, around 41% of Americans have vitamin D insufficiency, meaning that their numbers don’t reach a deficiency level but aren’t optimal. “Many of us are not getting enough vitamin D daily from sun exposure. We don't spend as much time outside or are more aware of the dangers of too much sun exposure. So we wear hats, put on sunscreen, and try to stay in the shade,” says Gillean Barkyoumb, M.S., RDN. “The signs and symptoms of vitamin deficiency in adults—fatigue, bone pain, muscle soreness or mood changes—can easily be missed. Anyone who is over the age of 65, has dark-colored skin, or is homebound and unable to use sun exposure as a source of vitamin D should consider taking a vitamin D supplement.”
Other factors, such as season or even the environment, can also cause deficient levels.
“Our skin can synthesize vitamin D3 via UVB sunlight exposure, but various factors like skin melanin content, air pollution, weather variations, sunscreen use and geographic location, among others, can affect how much we produce,” says Huma Chaudhry, RD, LDN.
Another way to obtain vitamin D is through food, such as fatty fish, egg yolks, mushrooms exposed to UV light, fortified cereals and milk. Because this particular food list is limited, getting enough vitamin D throughout the week can be difficult for many. “Most of us are not consuming a large quantity of these foods, which can make it difficult to get enough vitamin D from food alone,” Chaudhry continues.
8 Conditions That May Increase the Risk of Vitamin D Deficiency
1. Aging
As you age, you undergo a process of adding and losing bone density and mass. Before the age of 25, a person’s bone density will increase; then bone density remains pretty steady between the ages of 25 and 50. However, after age 50, bone breakdown (also known as resorption) will happen faster, so sufficient vitamin D and calcium to strengthen bones is vital for the older population.
Without a proper amount of these nutrients, skeletal effects due to reduced calcium absorption can result in a higher risk of falls and injuries. Production and metabolism of vitamin D change as you age, and older people are less likely to get the sun exposure needed. Research published in 2022 in Endocrine shows that, in this case, aging adults may benefit from low-dose vitamin D supplementation (around 25 micrograms a day).
2. Osteoporosis and Osteopenia
Your body constantly breaks down and rebuilds new bones as you age. If your body can’t keep up with new bone creation, it increases your risk of osteoporosis—a condition where your bones are too brittle and weak, increasing your risk of fractures, per the Centers for Disease Control and Prevention. While not as severe as osteoporosis, osteopenia, which is the loss of bone mineral density, also makes bones weaker.
“Vitamin D is popular for supporting our bone health and can be used to help treat bone conditions like osteoporosis and osteopenia,” says Chaudhry. “It plays a crucial role in keeping a homeostatic balance of important structural minerals, calcium and phosphorus.”
3. Neurological Diseases
A 2023 review in Biomedicine & Pharmacotherapy points out how vitamin D works as a neurosteroid in the body, which is essential for the development and functioning of one’s brain. Low levels of vitamin D have been associated with an increased risk of neurological illnesses such as Alzheimer's disease, Parkinson’s disease, epilepsy and multiple sclerosis.
4. Malabsorption Disorders
Certain malabsorption disorders, such as cystic fibrosis, celiac disease, short bowel syndrome and inflammatory bowel disease, can also result in a severe vitamin D deficiency, notes a 2015 review in the Journal of Digestive Diseases. These conditions make it difficult to digest and absorb certain nutrients. Due to this, people with malabsorption disorders may require supplementation to get an adequate amount of vitamin D and prevent other deficiency-related conditions.
5. Kidney and Liver Diseases
“Kidney and liver disease result in a reduction of the enzymes needed to convert vitamin D into a form that the body can use, which can lead to a deficiency,” says Barkyoumb.
Research has linked low serum vitamin D concentrations with potentially developing nonalcoholic fatty liver disease. A 2021 meta-analysis published in Frontiers of Pharmacology concluded that vitamin D supplementation could be considered an effective strategy for those managing NAFLD.
6. Depression
“Low vitamin D levels have been linked to increased symptoms of mood disorders like depression,” says Chaudhry. “Encouraging time in nature, adding vitamin D-rich foods to one’s diet, and a supplement can many times be added to one’s mental health treatment plan.”
7. Pregnancy
“Fetal vitamin D demands make it crucial for pregnant women to take in enough vitamin D,” says Jamie Adams, M.S., RD, LDN. “Repeated clinical research has demonstrated how vitamin D intake can improve fetal growth and development but also better health outcomes for moms. Vitamin D plays a crucial role in fetal development, bone health and immune function. Pregnant women often have increased demands for vitamin D to support the growing fetus and maintain their own health.”
A 2020 review in Current Opinion in Obstetrics and Gynecology points out that vitamin D supplementation may be wise during pregnancy. It can improve fetal growth while also reducing the risk of certain conditions, such as small-for-gestational-age, preeclampsia, preterm birth and gestational diabetes.
8. Rickets
Although bones are building more rapidly at a young age, there is still the possibility of disease if a child experiences severe vitamin D deficiency, known as rickets, per the NIH. If the child doesn’t absorb enough calcium and phosphorus through food and is deficient in vitamin D, it can cause soft and weakened bones.
“A vitamin D-rich diet and supplement routine can be a necessary part of treatment,” says Chaudhry.
Benefits of Vitamin D Supplementation
Thankfully, vitamin D supplementation is possible and easily accessible. Vitamin D supplements can provide sufficient vitamin D for the day or week. Because vitamin D is a fat-soluble vitamin—helping the body maintain calcium and phosphorus through fat absorption—it doesn’t flush out of your system when you urinate like a water-soluble vitamin, which means you can take a higher amount of vitamin D once or twice a week to get a sufficient amount, versus taking it every day.
“When shopping for a vitamin D supplement, you want to look for vitamin D3, cholecalciferol, the more easily absorbed and utilized form of vitamin D,” says Stokes.
Deciding how much to take is a conversation that is best to have with a health care professional who knows your particular needs, as well as your health habits and how often you are being exposed to vitamin D without supplementation already.
Recommended Daily Intake and Dosage Guidelines
To get sufficient vitamin D, the recommended dietary allowance for the average person (ages 1 to 70) is 15 micrograms (or 600 IU) daily. Adults 71 and over should get 20 micrograms (800 IU). However, as previously mentioned, since getting enough sunlight exposure or vitamin D through dietary sources may not be possible, a supplement may be wise.
That said, the amount of vitamin D you should take from a supplement depends on many factors. So, your best bet is to consult your health care provider before starting supplementation to determine the appropriate dosage for you.
“The most important factor for knowing which vitamin D supplement is best for you is to have your levels tested. It's an easy blood test and your result will help you and your doctor to determine the potency and frequency of vitamin D supplementation,” says Stokes.
The Bottom Line
Vitamin D is easily accessible thanks to sun exposure, but particular circumstances can complicate getting the recommended daily amount. Besides food sources, vitamin D supplementation could be wise for those with particular conditions such as neurological disease, kidney or liver disease, malabsorption disorders, rickets, or even mental health conditions such as depression. Getting the proper amount of vitamin D is also crucial during aging and pregnancy to avoid the risk of injuries or fetal conditions.
However, with so many different factors at play, it’s crucial to consult a health care professional to get the best advice for vitamin D supplementation for your specific needs.