Where it comes from: Vitamin D is a group of fat-soluble prohormones that's introduced to your body through delicious dietary sources such as fish, eggs, fortified milk and not-so-delicious cod liver oil. The sun is also considered a source, as exposure to UV rays triggers the body to produce vitamin D naturally.
There are two important forms of vitamin D to note: ergocalciferol (vitamin D2) and cholecalciferol (vitamin D3). They're collectively known as Calcitriol and play an important role in the maintenance of several organ systems.
What it'll do for you: Vitamin D's main job is to increase the flow of calcium into the bloodstream by promoting the absorption of calcium and phosphates from food in the intestines and the reabsorption of calcium in the kidneys. That means vitamin D plays a key role in maintaining strong bones and protecting against osteoporosis. Experts and recent studies say Vitamin D plays a role in a few other positive effects as well:
- Improves longevity
Studies of more than 57,000 subjects found that people taking supplements with at least at least 500 IUS of vitamin D were seven percent less likely to die than those who didn't take daily supplements. Researchers credited this to the protective effect of vitamin D against diseases—including cancer—and the vitamin's possible boost of blood vessel efficiency and the immune system.
- Lowers the risk of heart disease
Researchers at the Intermountain Medical Center Heart Institute in Murray, Utah, studied 9,400 patients whose blood tests revealed low vitamin D levels during a routine trip to the doctor. The patients who raised their vitamin D levels by their next follow-up were 33 percent less likely to have a heart attack and 20 percent less likely to develop heart failure compared to their counterparts who did not increase vitamin D levels.
- Prevents high blood pressure
It has been noted that blood pressure is often elevated during the winter—when the body is producing lower levels of vitamin D through sunlight. This suggests a possible direct correlation between higher levels of vitamin and low blood pressure levels.
- May lower risk of certain cancers
European researchers have found that people with higher blood levels of vitamin D have a much lower risk of colon cancer. In one study, doctors examined the lifestyles of more than 520,000 patients between 1992 and 1998. The results, which were reported in January of this year, found that those with the highest blood levels of vitamin D had a nearly 40 percent decrease in colorectal cancer compared to those with the lowest levels.
- Helps fight against influenza
After a four-month long study of Japanese schoolchildren, researchers found that taking vitamin D supplements during the winter and early spring help prevent seasonal flu and asthma attacks. There was no consideration of the effects of the supplements on adults but other studies have found that vitamin D dramatically stimulates natural killer cells and play a major role in protecting the lungs from infection.
- Reduces muscle pain
Limited research has reported vitamin D deficiency in patients with low-back pain, and that supplementation may help to reduce the pain. Supplements may also help with chronic fatigue, headaches and other types of pain.
Suggested intake: The recommended intake of vitamin D for males up to 50 years old is 200 IU (or 5 micrograms) and increases 200 IUs every 20 additional years. "The average man seems to be deficient in many vitamins, especially vitamin D," says registered dietitian and American Dietetic Association spokesperson Jim White. Not surprisingly, he recommends a varied diet. White adds that the richest sources of vitamin D are egg yolks, some types of fish (salmon, tuna and mackerel), butter, liver and cheese. "But it is important to stay within you calorie needs," White adds.
It's been reported that 10 to 15 minutes of sunshine three times a week is enough to prevent deficiencies. However, many people living in sunny climates still do not make enough vitamin D and need more from their diet or supplementation. "Individuals with limited sun exposure need to include good sources of vitamin D in their diet or take a supplement," White adds.
Those who take a multivitamin should note that most pills do include vitamin D, usually in strengths from 50 IU to 1,000 IU. White says supplements are okay to take but that you should consider the IUs you're already getting from your diet and work with your doctor to find a supplement that supplies the right amount of IU's for your diet or lifestyle.
How important is vitamin D? Deficiencies have now been linked to types of cancers, heart disease, depression, weight gain, muscle pain and other maladies. "Lack of vitamin D may lead to a condition called rickets, especially in children, in which bones and teeth are weak," explains White. "In adults it may cause a condition called osteomalacia, in which calcium is lost from bones so that they become weak. This is very rare in men but has been seen in extreme cases."
Associated risks/scrutiny: Too much vitamin D may lead to vitamin D toxicity, which is a buildup of calcium in the blood, causing symptoms such as nausea, vomiting, poor appetite, constipation, weakness, confusion, heart rhythm abnormalities and kidney stones. The calcium build up could also lead to kidney stones and calcium deposits in soft tissues such as the heart and lungs, reducing their ability to function.
Most cases of excessive amounts of vitamin come, not from sunlight or from foods, but from overdoses of supplements.