If there is a vitamin that gets busy going to work inside the human body, it is vitamin D. While all vitamins and minerals that are naturally found in our bodies are necessary to sustain life and keep us healthy, few are as versatile as vitamin D.
Vitamin D regulates the expression of more than one thousand genes in the human body! To start, it regulates levels of calcium and phosphorus in our blood, allowing for healthy bone growth. It is essential for the body’s absorption of calcium. Working synergistically with calcium, vitamin D helps prevent osteoporosis, brittle bones, rickets and osteomalacia. Rickets is a softening of bones that can lead to fractures and skeletal deformities; seen primarily in children, it can also happen in adults. Osteomalacia, a weakening of bones or muscles, occurs in adults.
Vitamin D is essential in maintaining heart health. It helps regulate heart beat and vascular pressure. Vitamin D deficiency is linked to cardiovascular disease, including high blood pressure, coronary artery disease, peripheral vascular disease and stroke.
More and more, vitamin D is also gaining attention as an immune system strengthener. In addition to helping the kidneys stay healthy, it activates genes in macrophages (a type of white blood cell), which in turn make antimicrobial peptides — natural antibiotics produced by the body. Like prescription antibiotics, these peptides attack and kill unfriendly bacteria; but unlike the prescription kind, they also kill viruses. When a person has low vitamin D blood levels, he or she will have fewer antimicrobial peptides and will be more prone to catching colds, the flu and various respiratory infections.
Vitamin D affects cell growth and the creation of new cells. It regulates proteins needed to cause normal cell growth and cell multiplication. When cells are damaged, they undergo apoptosis, or genetically programmed destruction, preventing harm to the body. If not enough vitamin D is in our blood, apoptosis may be disrupted, leading to illnesses or even tumor growth. Perhaps as a result of this, vitamin D is now believed to help prevent different types of cancer, including skin and colon cancers.
Vitamin D deficiency is also believed to be a risk factor for types 1 and 2 diabetes, seasonal affective disorder, and depression.
Where Can Vitamin D Be Found?
The most abundant source of vitamin D, as well as the cheapest, is sunshine.
Glands in the lowest layer of the skin use ultraviolet radiation from the sun to make “pre-vitamin D,” which the liver and kidneys convert to vitamin D.
Experts calculate that a fair-skinned person only needs some 20 minutes of sunshine a day (without sunscreen and with as much skin exposure as possible), to get an ample daily supply of vitamin D. A dark-skinned person needs about 10 times that, or 2 hours. Children should get some daily sun, also, as a child who is regularly exposed to sunlight is less likely to catch colds.
But in overcast climates, or in the winter at higher latitudes, or when someone is too busy working or otherwise indisposed, it would be difficult to get daily sun exposure. In such cases, people can strive to get as much vitamin D as possible from dietary sources, as well as from supplements.
The following foods are some of the highest in vitamin D:
- Fatty fish, including salmon, swordfish, tuna, sardines, and sole
- Enriched dairy foods: milk, cheese, yogurt, etc.
- Eggs: whites have calcium, yolks have vitamin D, so be sure to eat the whole egg!
- Beef liver
- Mushrooms: though all varieties offer some vitamin D (as well as antioxidants and dietary fiber), portobello and shiitake have by far higher vitamin D content than most other varieties, especially when they’re dried in the sun. Just like our skin, mushrooms have the amazing ability to gather UV radiation and store it!
How Much Vitamin D Is Enough?
Because foods contain relatively low amounts of vitamin D, many experts advise that people take supplements, in addition to dietary consumption.
The United States government’s recommended daily allowance for vitamin D is 400 international units (IUs). That’s certainly enough to prevent rickets and osteomalacia; but many health experts believe that if you want to reap the full benefits of this powerhouse vitamin, you should up your intake quite a bit.
The Institute of Medicine, and a handful of other health organizations, recommend that a person not take more than 4,000 daily IUs. But to get close to this amount, you would have to take supplements, as foods come in at considerably less (consider that an 8-oz glass of enriched milk contains only 100 IUs).
Some experts set the limit at about 5,000 IUs a day; doses that are too large can result in vitamin D toxicity. This can lead to calcium being deposited in soft tissues like the heart and lungs, which could impair their function. D toxicity could also cause nausea, vomiting and constipation.
Following these guidelines should help you reap the benefits of vitamin D, without any dangers. And it appears that a large percentage of us could stand to increase our vitamin D intake: while studies evaluating vitamin D deficiency among Americans continue being done, and their results vary, researchers believe that one-third or more of all Caucasians in the U.S. are D-deficient or close to deficient, along with an even greater percentage of Hispanics, and as many as 80 percent of all African Americans. Only one percent of Americans in one study were found to have too much vitamin D.
By Marc Courtiol