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Vitamin D is one of the four major fat-soluble vitamins your body needs to perform at its best. Adequate levels of vitamin D are associated with better immune health, cardiovascular health, cell growth regulation and anti-inflammatory action throughout the body.¹ Recent research even suggests that vitamin D may also play a part in weight loss and in preventing depression.²³
This micronutrient is often called the sunshine vitamin because our skin can naturally produce it when exposed to sunlight.⁴ Vitamin D is also available from a variety of food sources. So why are roughly 40% of Americans vitamin D-deficient?⁵
Unfortunately, it’s difficult to get enough vitamin D from diet alone, and getting enough from the sun comes with an increased risk of skin cancer, heat exhaustion, skin damage, and even immunosuppression when exposed to high levels of UV radiation.⁶
The trick to achieving the right balance is understanding how much vitamin D you’re regularly getting and how to safely get more from the sun if needed.
How does vitamin D work?
The primary role of vitamin D is to help your body absorb calcium and phosphorus. These two vital minerals keep your muscles, teeth, and bones healthy and strong.⁷⁸
Vitamin D also helps your immune cells fight off viruses, bacteria and other harmful pathogens and helps your nerves relay messages from your brain.⁹¹⁰
Vitamin D comes in two main forms:¹¹
- Vitamin D2 (ergocalciferol): D2 is derived from fungi-based dietary sources, namely mushrooms.
- Vitamin D3 (cholecalciferol): D3 is found in animal products, especially beef liver, egg yolk, cod liver oil and other oily fish.¹² D3 is the form of vitamin D you produce with exposure to sunlight.
It’s hard to get enough vitamin D from food alone — a typical adult’s recommended daily intake (RDI) of vitamin D is 15mcg (600 IU).¹³ Additional sources of vitamin D include sunlight, dietary supplements and specially fortified foods.¹⁴
Vitamin D deficiency
It’s easy to overlook the importance of vitamin D until you are diagnosed with a deficiency. With normal vitamin D levels, your intestines absorb 30 to 40% of your dietary calcium. But if you’re vitamin D deficient, your intestinal absorption of dietary calcium drops to 10 to 15%.¹⁵
Among other conditions, such as tooth decay or a weak immune system, low vitamin D levels and inefficient calcium absorption are linked to osteomalacia in adults and rickets in children. These diseases cause bones to become thin, brittle and fracture-prone, leading to chronic pain, bowed legs and motion problems.¹⁶ Although both conditions have become rare thanks to vitamin D-fortified foods, cases of osteoporosis — another bone-thinning condition — are increasing as the population ages.¹⁷
How much vitamin D do you need?
Your vitamin D requirements increase with age. Getting your daily dose will reduce your risk of vitamin D deficiency and related complications.
Infants under 12 months
It is recommended that infants get at least 400 international units (IU) daily until their first birthday.¹⁸ Infants should not be exposed to direct sunlight until after six months of age.¹⁹
Since formulas are already supplemented with vitamin D, formula-fed babies do not need additional supplementation as long as they drink about 34 ounces a day.²⁰
To ensure breastfed infants have sufficient vitamin D in their bodies, healthcare providers may recommend vitamin D supplements for infants or their nursing mothers.²¹
One to 70 years old
Anyone from one to 70 years of age (including pregnant women) is advised to get a daily vitamin D intake of 600 IU unless advised otherwise by a medical professional.²² This is especially important for anyone in the following groups who struggle to maintain adequate vitamin D levels:²³
- Adults over 65 years old
- Darker-skinned individuals (commonly those of South Asian, African-Caribbean, and African descent)
- Overweight and obese individuals with digestive disorders (such as celiac disease or Crohn’s disease)
Over 70 years old
Individuals aged 71 years and older are advised to get at least 800 IU of vitamin D per day.²⁴ As we age, our risk for vitamin D deficiency increases because our bodies tend to synthesize less vitamin D from the sun. Our kidneys also become less efficient in transforming vitamin D2 and D3 to the active form that the body needs.²⁵
How much sun is needed for vitamin D?
Due to associated health risks with sun exposure, the American Dermatology Association recommends relying on foods that are naturally rich in vitamin D, fortified foods and supplements.²⁶
For those who do want to get vitamin D from the sun, follow these sun-safe tips:²⁷
1. Pick the right time of day
Most people in the U.S. get their sun fix between spring and late fall before the darker winter months set in. During that time, the summer months remain the best time to soak up the most sunshine, but this practice requires some caution.
The UV index (UVI) and corresponding UV intensity measure the ultraviolet B (UVB) rays from the sun — a higher UVI increases your risk of sun damage. To prevent skin damage, stay hydrated and limit exposure time: less than 30 minutes for a moderate UV rating, and avoid exposure during peak hours (between 11 a.m. and 3 p.m.) when the rating is high.²⁸
2. Be conscious of your skin type
Vitamin D deficiency is more common in African American and non-white Hispanic communities because individuals with darker skin shades have higher amounts of the pigment melanin.²⁹³⁰ Melanin acts as a first line of defense against UV rays and protects against skin cancer, sunburns and skin damage.³¹ In terms of vitamin D, however, melanin also creates a barrier for UVB rays, making it harder for the body to produce vitamin D with small amounts of sunshine.
3. Expose more skin to speed up vitamin D production
The more skin you expose to sunlight, the more UVB rays are absorbed, which may result in higher production of vitamin D and a higher vitamin D status. (But again, sun exposure should be done safely — consider wearing a wide-brimmed hat and sunglasses to safeguard eyes and face.)
While there is no one-size-fits-all guideline for sun exposure, between five to 15 minutes, three times a week at moderate ratings from spring to fall, should be sufficient for most individuals.³²³³
4. Try short bouts of sun exposure
Sunscreen plays a crucial role in protecting us from skin cancer and sunburns, not to mention premature aging. A typical sunscreen contains a chemical blend that helps absorb, reflect, or diffuse sunlight, preventing harmful ultraviolet rays from reaching your skin cells. However, it also blocks the UV rays needed to make vitamin D.
Balancing time with and without sunscreen to prevent long-term sun damage is key, so sticking to short periods of unprotected sun exposure provides your body with the best of both worlds. Then, thoroughly apply sunblock! Choose a broad-spectrum sunscreen with a minimum sun protection factor (SPF) of 30 to protect against UVA and UVB rays.
What happens if you don’t get enough vitamin D?
The short- and long-term effects of vitamin D deficiency can be serious. Here are some common symptoms and health complications you may experience if you don’t have enough vitamin D.
1. Fatigue
Low vitamin D levels (vitamin D insufficiency and deficiency) can affect your energy levels and cause feelings of lethargy, weakness and fatigue.³⁴³⁵ A healthcare practitioner may recommend vitamin D supplementation to relieve feelings of excessive tiredness caused by a deficiency.
2. Weakened immune system
If you get sick frequently, low levels of vitamin D could be contributing to a weakened immune system. This is due to vitamin D’s direct interactions with disease-fighting immune cells, like T cells and B cells, through the vitamin D receptor (VDR).³⁶³⁷ By extension, vitamin D deficiency contributes to the improper functioning of important immune defense systems, leaving your body prone to pathogens and inflammation.
Studies have also noted a relationship between low vitamin D blood levels and pneumonia, bronchitis, chronic lung disorder, and other respiratory tract infections.³⁸
3. Bone and back pain
Vitamin D deficiency can weaken your skeletal health. After all, the micronutrient plays a major role in the absorption of two pro-bone health minerals: phosphorus and calcium. Low bone calcium reserves cause low bone density and osteoporosis — leading to chronic joint, back, and bone pain, plus an increased risk of falls and fractures.³⁹
4. Depression
Vitamin D deficiency may contribute to clinical depression or other mood problems.⁴⁰ Research indicates that vitamin D could play a role in helping with depression symptoms, especially in older adults.⁴¹
5. May impact wound healing
Vitamin D’s ability to fight infection and control inflammation may help heal wounds. A 2016 investigation established that the vitamin could increase the production of compounds that help form new skin during the wound-healing process.⁴² So, if your wounds heal unusually slowly after an injury, infection, or surgery, you may want to investigate your vitamin D levels.
6. Unexplained muscle pain
The active form of vitamin D plays a crucial role in facilitating healthy communication throughout your body. Without robust communication between the brain and various body parts, your central nervous system wouldn't be able to tell the muscles when to move. As a result, vitamin D deficiency has been cited as a potential cause of unexplained headaches and muscle pain in both kids and adults.⁴³
Can you have too much vitamin D?
Let’s be clear: you can’t get too much vitamin D from the sun.
Healthy adults can safely take up to 100 mcg (4,000 IU) of daily vitamin D supplements without any notable side effects.⁴⁴ Some studies suggest that even higher levels won’t put healthy adults at risk of harm, although more research is needed.⁴⁵ While vitamin D toxicity is very rare, it typically only occurs with unreasonably high doses of vitamin D supplements (more than 50,000 IU)⁴⁶ every day for several weeks or more. Even then, the common symptoms — which include high blood pressure, constipation, abdominal pain, vomiting, drowsiness and confusion⁴⁷ — are rarely life-threatening in otherwise healthy adults when treated quickly.
Summary
Roughly 40% of Americans are vitamin D deficient. Low levels of this essential vitamin can lead to adverse health outcomes, including excessive fatigue, a weakened immune system, depression, bone weakness and muscle pain.
In addition to dietary supplements and fortified foods, you can help enhance your vitamin D intake with safe and short bouts of sun exposure.
