In the intestines, the receptors capture vitamin D, enabling efficient calcium absorption. But similar receptors are also present in many other organs, from the prostate to the heart, blood vessels, muscles, and endocrine glands. And work in progress suggests that good things happen when vitamin D binds to these receptors.
The main requirement is to have enough vitamin D, but many Americans don't. Vitamin D deficiencies were rare when most men rolled up their sleeves to work in sunny fields.
But as work shifted from farms to offices, that changed. Deficiencies are also common in patients with intestinal disorders that limit absorption of fat and those with kidney or liver diseases that reduce the conversion of vitamin D to its active form, calcitriol 1,25 OH 2D. In addition, certain medications reduce the availability or activity of vitamin D. And even in healthy people, advancing age is linked to an increased risk of vitamin D deficiency. A number of factors can play a role.
Limited exposure to sunlight heads the list. Except during the short summer months, people who live at latitudes above 37 degrees north or below 37 degrees south of the equator don't get enough UVB energy from the sun to make all the vitamin D they need.
The same is true for people who spend most of their time indoors and for those of us who avoid sunshine and use sunscreens to protect our skin from the harmful effects of ultraviolet radiation see box below.
It's an example of an unforeseen consequence of wise behavior, but you can enjoy sun protection and strong bones, too, by taking vitamin supplements. Like politicians, doctors often have to compromise; when it comes to sunshine, most pols promise blue skies, while most docs turn out to be the shady guys — or, at least, sunscreen advocates. UVB provides the energy your skin needs to make vitamin D, but that energy can burn the skin and increase the cell damage that leads to cancer.
UVA also contributes to skin damage and premature aging. To protect yourself, avoid the summer sunshine, especially between 10 a. Whenever possible, wear a large-brimmed hat and a tightly woven, dark-colored long-sleeve shirt and long pants when you go out in the sun. But summer garb is usually lightweight and exposes a lot of skin.
That's where a sunscreen comes in. Look for a product with an SPF of 30 or higher. Apply your sunscreen early, often, and liberally. These many factors explain why vitamin D deficiencies are shockingly common in the United States. 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. That's what spurred a recommendation from the American Academy of Pediatrics that every breastfed infant be given vitamin D if they're being given liquid multivitamin drops, they're getting enough of it.
There are claims that one needs to get a certain amount of sun exposure every day in order to produce enough vitamin D to be healthy. The majority of people can get their vitamin D from nutritional supplements and from vitamin D-fortified foods.
There are some people who are typically not dermatologists or experts in the biology of skin cancer who have advocated for tanning to get vitamin D. But we know that UVB light causes skin cancer and that protecting yourself against it makes sense.
As a doctor who treats patients who have melanomas, I want the general public to be advised that under no circumstances can use of a tanning bed or tanning in general be justified on the basis of vitamin D.
Take a supplement instead. Click here for more information about Yale Medicine's Endocrinology Department. Or to make an appointment call Skip to Main Content. Doctors tell you what you need to know about vitamin D. What they have to say may surprise you. The short answer is from food, the sun or supplements.
The more vitamin D you take, the better? Absolutely not. Cancer Vitamin D does not seem to reduce the risk of developing cancer of the breast, colon, rectum, or lung.
It is not clear whether vitamin D affects the risk of prostate cancer or chance of surviving this cancer. Very high blood levels of vitamin D may even increase the risk of pancreatic cancer.
Clinical trials suggest that while vitamin D supplements with or without calcium may not affect your risk of getting cancer, they might slightly reduce your risk of dying from this disease. More research is needed to better understand the role that vitamin D plays in cancer prevention and cancer-related death. Heart disease Vitamin D is important for a healthy heart and blood vessels and for normal blood pressure. Some studies show that vitamin D supplements might help reduce blood cholesterol levels and high blood pressure —two of the main risk factors for heart disease.
Other studies show no benefits. If you are overweight or obese , taking vitamin D at doses above 20 mcg IU per day plus calcium might actually raise your blood pressure. Overall, clinical trials find that vitamin D supplements do not reduce the risk of developing heart disease or dying from it, even if you have low blood levels of the vitamin.
Depression Vitamin D is needed for your brain to function properly. Some studies have found links between low blood levels of vitamin D and an increased risk of depression. However, clinical trials show that taking vitamin D supplements does not prevent or ease symptoms of depression. Multiple sclerosis People who live near the equator have more sun exposure and higher vitamin D levels. They also rarely develop multiple sclerosis MS , a disease that affects the nerves that carry messages from the brain to the rest of the body.
Many studies find a link between low blood vitamin D levels and the risk of developing MS. However, scientists have not actually studied whether vitamin D supplements can prevent MS.
In people who have MS, clinical trials show that taking vitamin D supplements does not keep symptoms from getting worse or coming back. Type 2 diabetes Vitamin D helps your body regulate blood sugar levels.
However, clinical trials in people with and without diabetes show that supplemental vitamin D does not improve blood sugar levels, insulin resistance , or hemoglobin A1c levels the average level of blood sugar over the past 3 months. Weight loss Taking vitamin D supplements or eating foods that are rich in vitamin D does not help you lose weight. Yes, getting too much vitamin D can be harmful. Extremely high levels of vitamin D can cause kidney failure , irregular heartbeat, and even death. High levels of vitamin D are almost always caused by consuming excessive amounts of vitamin D from dietary supplements.
You cannot get too much vitamin D from sunshine because your skin limits the amount of vitamin D it makes. The daily upper limits for vitamin D include intakes from all sources—food, beverages, and supplements—and are listed below in micrograms mcg and international units IU :. Yes, vitamin D supplements may interact with some medicines.
Here are several examples:. Tell your doctor, pharmacist, and other healthcare providers about any dietary supplements and prescription or over-the-counter medicines you take.
They can tell you if the dietary supplements might interact with your medicines.
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