The media has given vitamin D an awful lot of attention lately, almost to the point of overdoing it. It seems like this oft-forgotten vitamin has appeared out of the woodwork with its head held high, on a crusade to battle all kinds of diseases. Many health experts are even claiming that the recommended intake for vitamin is too low. Let’s take a closer look and learn what vitamin D is all about.
What is Vitamin D?
Vitamin D, a fat-soluble vitamin, is sometimes called the “sunshine vitamin” because it’s made in the body when ultraviolet rays from the sun come in contact with the skin. Surprisingly, perhaps, this vitamin isn’t found in too many foods—salmon, mackerel, tuna, sardines, and cod liver oil are the main sources. Milk, margarine, and some cereals, yogurts, and orange juices are fortified with vitamin D; small amounts are also found in eggs and liver. Of course, vitamin D is available as a dietary supplement as well.
Vitamin D has to undergo some changes, biologically, before it can be used by the body. When you ingest vitamin D from food or supplements, or when you obtain vitamin D from the sun, the vitamin undergoes a conversion in the liver to a form called 25-hydroxyvitamin D. Then, this form of the vitamin gets converted in the kidneys to the active form that the body can actually use, called 1, 25-dihydroxyvitamin D, or calcitriol. Calcitriol is actually a steroid hormone, and vitamin D is sometimes called a precursor hormone, or the building block, for calcitriol.
What Does Vitamin D Do?
Miracles aside for a moment, one of vitamin D’s main roles in the body is to help maintain bone health. Vitamin D is required for calcium absorption in the intestines and to maintain the balance of calcium and phosphate in the body for bone mineralization.
We also need vitamin D for normal bone growth. You’ve probably heard of rickets, a bone disease that occurs in children due to a deficiency of this vitamin. Insufficient vitamin D leads to softening and weakening of bones. Rickets can manifest itself in the form of bow legs or a curving of the spine.
Osteomalacia is bone-softening that occurs in adults. Bone pain and muscle weakness are the main symptoms of this disease. Osteomalacia isn’t the same as osteoporosis, however. Osteomalacia results from a deficiency of vitamin D, which, in turn, affects the building of bones. Osteoporosis affects already-constructed bones.
Besides bone health, vitamin D plays a role in the function of the immune system and helps to reduce inflammation. Also, vitamin D is found in just about every cell in the body, meaning that this vitamin is needed for cell differentiation and growth.
How Much Vitamin D Do You Need?
Here’s where part of the debate comes in. The Dietary Reference Intakes (DRIs) for vitamin D vary, based on age:
- Birth to 50 years: 200 international units (IU)
- 51 to 70 years: 400 IU
- 71+: 600 IU
Pregnant and lactating women need 200 IU of vitamin D.
Three and a half ounces of salmon contains 360 IU, 3 ounces of canned tuna in oil contains 200 IU, and 8 ounces of fortified skim milk contains 98 IU. Cod liver oil tops the charts at 1,360 IU per tablespoon; however, cod liver oil has its own set of potential problems, so it’s really not recommended to take this unless you’re careful and obtain it from a reputable source.
Are the DRIs for vitamin D high enough? The feeling from the medical community lately is that the established requirements for vitamin D aren’t enough, and that an intake between 800 to 1,000 IU would be better to aim for, especially for people at risk for deficiency, including older adults, those with limited sun exposure, those with gastrointestinal disorders, and people with darker skin.
More on vitamin D next week!