What is Vitamin D?
A fat-soluble vitamin, Vitamin D is a little different in that our bodies are able to synthesize it from cholesterol, making it a nonessential nutrient. That means we don’t technically need to get Vitamin D from our diet, but it certainly doesn’t hurt! (Plus, as we’ll see later, some people need Vitamin D supplementation because of where they live!)
Related Reading: Lipids (aka fats!)
There are two forms of the vitamin – Vitamin D2, which comes primarily from plant foods, and Vitamin D3, derived from animal foods or by our body’s own creation. Once the body has synthesized Vitamin D to its active form, it is actually a hormone (a compound that causes other parts of the body to act)!
Lots of research shows that Vitamin D3 is far superior in that the body can utilize it better than D2. Many foods might be fortified with Vitamin D or claim to be a good source, but are actually providing D2. Soy milk is notorious for this claim, and our bodies are hardly getting any benefit from the levels of the inferior form of this vitamin. (Read the label on the back to see which form of Vitamin D with which the product is being fortified!)
The RDA for adults up to age 70 is 15 micrograms/day (600 IU/day), and for adults over 70, 20 micrograms/day (800 IU/day). (IU is the term usually found on supplements.)
What does Vitamin D do in the body?
The vitamin plays a large role in the health of our intestines, kidneys, and, of course, our bones.
The bones require many nutrients to work together in order to stay strong, including Vitamin A and Vitamin K, calcium, phosphorus, magnesium, and fluoride. Vitamin D assists by increasing the absorption of calcium and phosphorus into the bloodstream. The abundance of these minerals in the blood allow the bones to keep their stores as well as take from the blood, which causes growth and maintenance of the bones.
If these minerals are not being taken in in large enough amounts, Vitamin D, acting as a hormone, will tell the kidneys to reabsorb these nutrients (rather than excrete them), or even release the minerals from the bones if they are needed in other parts of the body.
Because 90% of our Vitamin D supply comes from our own body – which requires the sun – there are some factors that could increase your risk for deficiency. Having dark skin or a low exposure to sunlight would increase your Vitamin D needs. Breastfeeding without supplementation can also lead to a Vitamin D deficiency.
The absorption of calcium is affected negatively, even if calcium intake is adequate. This will lead to a low concentration of calcium in the blood, and so the bones’ mineral stores will be depleted.
Rickets is common in children, and is a condition where the bones do not calcify (harden) normally. This results in abnormal growth and deformities of the bones. Bowed legs are a result of soft bones attempting to support the weight of the child’s body. Ribs with what appears to be beads on them is another symptom, as the bones fail to attach to cartilage properly.
Osteoporosis and osteomalacia are issues that older adults face, where the bones become brittle and soft due to the loss of mineral stores. These bones fracture easily.
While very difficult to consume toxic levels of Vitamin D through food and the body’s synthesis, supplementation of the vitamin can cause harmful effects. With a high consumption of Vitamin D comes a high concentration of calcium in the blood. The body will look for places to store the excess calcium, and will turn to the soft tissues of the body, calcifying them. This leads to stones, especially in the kidneys, and hardened tissues. Hardened blood vessels are a cause for concern, especially in the major arteries.
Where can I find Vitamin D in the diet?
Fortified milk is a good source of Vitamin D, but there are other sources for those who choose not to drink milk. The best natural food sources of the vitamin include salmon, sardines, and egg yolk. These high-fat foods have high concentrations of the fat-soluble vitamin.
Still, only about 10% of your Vitamin D intake will be coming from foods. The best source of the vitamin is made by your body, with the help of the sun.
While too much sun can cause sunburn, you won’t overdose on Vitamin D. That’s because its precursor will be killed off with overexposure to the sun, so the conversion rate to active Vitamin D will stay at safe levels. Only 5-10 minutes of sun exposure three times per week is enough to meet your Vitamin D needs! Remember, if your skin has a darker tone or you’re using sunblock, you’ll need to stay out a little longer.
Related Reading: Focus on Food – Eggs!
The 40° Latitude Issue
While the sun is our best source for Vitamin D, it isn’t a perfect system! Due to the way the sun’s rays hit the earth, there is a “sweet spot” between 40° north latitude and 40° south latitude where synthesis occurs year-round. However, above and below these lines and toward the poles, creation of Vitamin D basically stops for four to six months out of the year! (I’m looking at you, Canadians!) In this case, supplementation of Vitamin D is essential.
Do you get outside often enough to get your daily dose of Vitamin D, or are you one of those people who live above 40° North (or below 40° South) who need supplementation during the winter months? I do!