Vitamin D is a fat-soluble vitamin that is naturally present in very few foods, added to others, and available as a dietary supplement. It is also produced endogenously when ultraviolet rays from sunlight strike the skin and trigger vitamin D synthesis. Vitamin D obtained from sun exposure, food, and supplements is biologically inert and must undergo two hydroxylations in the body for activation. The first occurs in the liver and the second occurs primarily in the kidney.
Vitamin D promotes calcium absorption in the gut and it is also needed for bone growth and bone remodeling by osteoblasts and osteoclasts . Without sufficient vitamin D, bones can become thin, brittle, or misshapen. Vitamin D sufficiency prevents rickets in children and osteomalacia in adults . Together with calcium, vitamin D also helps protect older adults from osteoporosis.
Vitamin D has other roles in the body, including modulation of cell growth, neuromuscular and immune function, and reduction of inflammation . Many genes encoding proteins that regulate cell proliferation, differentiation, and apoptosis are modulated in part by vitamin D .
Think about vitamin D when you’re catching up on summer rays. It’s sometimes called the “sunshine vitamin” because it’s produced in your skin in response to sunlight. Vitamin D is a fat-soluble vitamin in a family of compounds that includes vitamins D-1, D-2, and D-3. It can affect as many as 2,000 genes in the body.
Vitamin D has several important functions. Perhaps the most vital are regulating the absorption of calcium and phosphorous, and facilitating normal immune system function. Getting a sufficient amount of vitamin D is important for normal growth and development of bones and teeth, as well as improved resistance against certain diseases. If your body doesn’t get enough vitamin D, you’re at risk of developing bone abnormalities such as soft bones (osteomalacia) or fragile bones (osteoporosis).
D fights disease
In addition to its primary benefits, research suggests that vitamin D may also play a role in:
- reducing your risk of multiple sclerosis, according to a 2006 study published in the Journal of the American Medical Association
- decreasing your chance of developing heart disease, according to 2008 findings published in Circulation
- helping to reduce your likelihood of developing the flu, according to 2010 research published in the American Journal of Clinical Nutrition
D fights depression
Research has shown that vitamin D might play an important role in regulating mood and warding off depression. In one study, scientists found that people with depression who received vitamin D supplements noticed an improvement in their symptoms.
In another study of people with fibromyalgia, researchers found vitamin D deficiency was more common in those who were also experiencing anxiety and depression.
D boosts weight loss
Consider adding vitamin D supplements to your diet if you’re trying to lose weight or prevent heart disease.
In one study, people who took a daily vitamin D supplement did not lose a significant amount of weight, but were able to improve their heart disease risk markers.
In another study, people taking a daily calcium and vitamin D supplement were able to lose more weight than subjects taking a placebo supplement. The scientists said the extra calcium and vitamin D had an appetite suppressing effect.
How do you get it?
Your body produces vitamin D naturally when it is directly exposed to sunlight. A little can go a long way. All you need is 10 minutes a day of midday, pre-sunscreen sun exposure, especially if you have fair skin.
Besides getting vitamin D through sunlight, you can also get it through certain foods and supplements to ensure adequate levels of the vitamin in your blood.
Beware of “D-deficiency ”
Many lifestyle and environmental factors can affect your ability to get sufficient amounts of vitamin D through the sun alone. These factors include:
- use of sunscreen
- spending more time indoors
- living in big cities where buildings block sunlight
- having darker skin
These factors contribute to vitamin D deficiency in an increasing number of people. That’s why it’s important to get some of your vitamin D from sources besides sunlight.
The symptoms of a vitamin D deficiency in adults include:
- general tiredness, aches and pains, and a general sense of not feeling well
- severe bone or muscle pain or weakness that may cause difficulty climbing stairs or getting up from the floor or a low chair, or cause the person to walk with a waddling gait
- stress fractures, especially in the legs, pelvis, and hips
Doctors can diagnose a vitamin D deficiency by performing a simple blood test. If you have a deficiency, your doctor may order X-rays to check the strength of your bones.
What to do if you’re deficient
If you’re diagnosed with a vitamin D deficiency, your doctor will likely recommend you take daily vitamin D supplements. If you have a severe deficiency, they may recommend you take high-dose vitamin D tablets or liquids. You should also make sure to get vitamin D through sunlight and the foods you eat.
Food sources of D
Few foods contain vitamin D naturally. Because of this, some foods are fortified. This means that vitamin D has been added. Foods that contain vitamin D include:
- egg yolk
- milk (fortified)
- cereal (fortified)
- yogurt (fortified)
- orange juice (fortified)
It can be hard to get enough vitamin D each day through sun exposure and food alone, so taking vitamin D supplements can help.
How much do you need?
There has been some controversy over the amount of vitamin D needed for healthy functioning. Recent research indicates that you need more vitamin D than was once thought. Normal blood serum levels range from 50 to 100 micrograms per deciliter. Depending on your blood level, your vitamin D intake needs may be increased.
The Institute of Food and Agricultural Sciences reports new intake recommendations based on international units (IUs) per day. IUs are a standard type of measurement for drugs and vitamins. IUs help experts determine recommended intake, toxicity, and deficiency levels for each person.
One IU is not the same for each type of vitamin. An IU is determined by how much of a substance produces an effect in your body. The recommended IUs for vitamin D are:
- children and teens: 600 IU
- adults up to age 70: 600 IU
- adults over age 70: 800 IU
- pregnant or breastfeeding women: 600 IU
Meet your needs for D
Some sources suggest that considerably higher daily amounts of vitamin D — as high as 2000 IU per day — are needed.
Although the exact amount may be in question, the importance of vitamin D is not. Talk to your doctor for guidance on how to ensure you get the right amount for your body might require.