The commonly recommended daily dose of vitamin D is IU 15 mcg 3. Not only is getting vitamin D around midday more efficient, but it might also be safer than getting sun later in the day. One study found that afternoon sun exposure may increase the risk of dangerous skin cancers 9. Midday is the best time to get vitamin D, as the sun is at its highest point and your body may manufacture it most efficiently around that time of day.
This means you may need less time in the sunlight at midday. People with darker skin typically have more melanin than people with lighter skin. Melanin helps protect the skin against damage from excess sunlight. However, that creates a big dilemma because darker-skinned people need to spend longer in the sun than lighter-skinned people to produce the same amount of vitamin D.
Studies estimate that darker-skinned people may need anywhere from 30 minutes to three hours longer to get sufficient vitamin D, compared to lighter-skinned people. This is a major reason why darker-skinned people have a higher risk of deficiency For that reason, if you have dark skin, you may need to spend a bit more time in the sun to get your daily dose of vitamin D.
Darker-skinned people have more melanin, a compound that protects against skin damage by reducing the amount of UVB light absorbed. Darker-skinned people need more time in sunlight to make the same amount of vitamin D as lighter-skinned people. So people who live farther away from the equator usually need to spend more time in the sun to produce enough People in Norway cannot make vitamin D from sunlight between October and March People who live farther away from the equator need more time in the sun, as more UVB rays are absorbed by the ozone layer in these areas.
During winter months, they cannot make vitamin D from sunlight, so they need to get it from foods or supplements. Vitamin D is made from cholesterol in the skin. That means you need to expose lots of skin to the sunlight to make enough. Some scientists recommend exposing around a third of the area of your skin to the sun 5.
According to this recommendation, wearing a tank top and shorts for 10—30 minutes three times per week during the summer should be sufficient for most people with lighter skin. People with darker skin may need a bit longer than this. Instead, try going without sunscreen for just the first 10—30 minutes, depending on how sensitive your skin is to sunlight, and apply sunscreen before you start burning. Since the head is a small part of the body, it will only produce a small amount of vitamin D.
You need to expose a sufficient amount of skin to sunlight to maintain healthy vitamin D blood levels. Wearing a tank top and shorts for 10—30 minutes three times per week is sufficient for lighter-skinned people, while those with darker skin may need longer. When this happens, the skin is exposed to lower levels of harmful UV rays However, because UVB rays are essential for making vitamin D, sunscreen could prevent the skin from producing it.
However, several studies have shown that wearing sunscreen only has a small impact on your blood levels during the summer 17 , 18 , And low levels of vitamin D are common even in apparently healthy young adults; in one study, more than a third of people between the ages of 18 and 29 were deficient. Numbers can never tell the whole story, but in this case, "D-ficiencies" add up to a wide range of health concerns. It's a paradox: Skeletal health is the best-known contribution of vitamin D, but it has also become the most controversial.
Although doctors agree that vitamin D deficiency increases the risk of osteoporosis and fractures, they disagree about the benefits and optimal dosage of supplements. Without enough vitamin D, the intestines cannot efficiently absorb calcium.
But because blood calcium is critical for neuromuscular and cardiac function, the body does not allow levels to fall. Instead, it pours out parathyroid hormone, which mobilizes calcium from bone. Blood calcium levels remain normal, so your heart and nerves keep working nicely.
But your bones bear the brunt: As bone calcium density falls, bones become weak and fracture-prone. Most studies show that a lack of vitamin D increases the risk of osteoporosis and the likelihood of hip and other non-spinal fractures. But there is considerable disagreement about how much supplements reduce the risk of fractures. Some studies include only women, others both men and women; some include only frail, elderly, or institutionalized subjects, others physically active people; some use vitamin D alone, others a combination of D and varying doses of calcium; and some administer international units IU of vitamin D a day, others up to IU a day.
Some men mistakenly dismiss osteoporosis as a women's worry, but none fail to recognize the importance of prostate cancer. Vitamin D has an important role in regulating cell growth. Laboratory experiments suggest that it helps prevent the unrestrained cell multiplication that characterizes cancer by reducing cell division, restricting tumor blood supply angiogenesis , increasing the death of cancer cells apoptosis , and limiting the spread of cancer cells metastasis.
Like many human tissues, the prostate has an abundant supply of vitamin D receptors. And, like some other tissues, it also contains enzymes that convert biologically inactive 25 OH D into the active form of the vitamin, 1,25 OH 2D.
These enzymes are much more active in normal prostate cells than in prostate cancer cells. In , Harvard's Health Professionals Follow-up Study of 47, men reported that a high consumption of calcium supplements was associated with an increased risk of advanced prostate cancer.
The risk was greatest in men getting more than 2, mg of calcium a day from a combination of supplements and food. Since then, other studies have confirmed a link between very high levels of calcium intake and increased risk, but they have exonerated dietary calcium consumption. The Harvard scientists speculate that the problem is not calcium itself but a relative lack of active vitamin D.
The risk of colon cancer , breast cancer, and other malignancies appears to rise in populations at latitudes far from the equator. Sun exposure and vitamin D levels may be part of the explanation. A recent clinical trial looking at a daily 1, IU vitamin D supplement did not show a decreased risk of cancer, but it was associated with a decreased risk of cancer death.
The most widely used recommended dietary allowance RDA for vitamin D is IU daily for adults up to age 69 and IU daily for people older than Is more better? Like the other fat-soluble vitamins, vitamin D is stored in the body's adipose fat tissue. That means your body can mobilize its own reserves if your daily intake falters temporarily — but it also means that excessive doses of vitamin D can build up to toxic levels.
At those extremes, vitamin D can raise blood calcium to levels that can cause grogginess, constipation , and even death. But it takes massive overdosing to produce toxicity.
You can make your vitamin D the old-fashioned way, by exposing your skin to UVB radiation in sunlight. It doesn't take much, but people living north of the degree-latitude line — roughly the imaginary line between Philadelphia and San Francisco — can't get enough UVB in winter to do the trick.
And many others will find it all too easy to overdose on UVB, increasing their risk of malignant melanomas and other skin cancers, as well as wrinkles and premature skin aging. When exposed to the sun, your skin can manufacture its own vitamin D. Leffell, MD , chief of Dermatologic Surgery. Another avenue to get vitamin D is by taking supplements.
These come in both pill and liquid form. They are generally recommended for people with fat absorption issues, lactose intolerance, milk allergies, as well as for people with darker skin tones or with certain medical conditions that prevent them from going outdoors. Through a process called hydroxylation, the liver and kidneys turn the stored vitamin D into the active form the body needs called calcitriol.
Those are the basic facts, but some questions might remain: How should you get vitamin D? How much should you get and when should you worry about your levels?
In light of these common questions, our Yale Medicine doctors help clear up some confusion about vitamin D, separating fact from fiction. Vitamin D is stored in fat. Modest increases above the RDA are not likely to cause harm. The child, who developed high blood calcium hypercalcemia , had to be hospitalized and treated with several types of medications to get the calcium levels down to normal levels.
You can now get 50, IU tablets over the counter. There are patients with specific issues who might need a prescription for high levels of vitamin D, but for most people, that amount will raise your vitamin D level too high. Babies should be getting smaller amounts in their first year of life, between and IU.
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