27 Jun 2016, 11:47 am
Focus on Vitamin D – The Sunshine Food (Issue 62)
It is summer. What better excuse for getting a tan, than getting your daily dose of vitamin D! Vitamin D is a unique vitamin since it can be made in your body when the skin is exposed to direct sunlight.
But how much sun do you actually need per day, and why do you need it at all?
WHY YOU NEED VITAMIN D
Vitamin D is so important that your body makes it by itself - but only after skin exposure to sufficient sunlight.
This important vitamin helps to maintain normal blood levels of calcium and phosphorus, which strengthen bones and teeth. (In other words, it helps your body to absorb calcium.) Vitamin D also helps regulate the immune system and the neuromuscular system and plays major roles in the life cycle of human cells.
HOW YOUR BODY USES IT
Vitamin D must undergo two chemical reactions in your body. When it enters the body, it is converted to calcidiol by the liver. The kidneys then convert calcidiol to calcitriol.
HOW MUCH YOU NEED
The RDA (Recommended Daily Allowance) is 600 IU. However, most experts recommend a dose of 1,000 IU per day for both infants and adults. Other sources argue that you may need at least double.
But first, what is IU? IU stands for International Units, which is the unit of measurement for fat-soluble vitamins. Biological equivalents, or 1 IU of vitamin D can be converted to .025 micrograms of vitamin D in the form of cholecalciferol.
The older you are, the more vitamin D you will need. There's also evidence that people with a lot of body fat need more than lean people.
SUN EXPOSURE AS A SOURCE
Exposing yourself to sunlight is the most important source of vitamin D because sunlight is far more likely to provide you with your daily requirement than food is. UV rays from the sun trigger vitamin D production in your skin. Lights from your home are not strong enough to produce vitamin D.
Depending on your skin type and the intensity of the sun, you are likely to need only between 4 and 20 minutes of direct sun exposure per day. Factors to consider are the following: Latitude; Day of the year; Time of day; Skin type; Ground surface type; Altitude.
For example, complete cloud cover halves the energy of UV rays, and shade reduces it by 60%. Industrial pollution also filters sun exposure.
Sunscreens with a sun protection factor (SPF) of 8 or greater will block UV rays that produce vitamin D. An initial exposure to sunlight of 10 to15 minutes allows you adequate time for vitamin D synthesis.
Ten to fifteen minutes of sun exposure at least twice per week to the face, arms, hands, or back without sunscreen is usually sufficient to provide adequate vitamin D.
Dark skin absorbs less sunlight, so people with dark skin do not get as much vitamin D from sun exposure as do light-skinned people.
Surprisingly few foods contain vitamin D -- unless it's added to the food.
The vitamin D super foods are Salmon and Mackerel. Other food sources include pure cod liver oil, tuna, sardines, beef or calf liver, egg yolks and cheese.
The recommended form of vitamin D is vitamin D3 (cholecalcifero). This is the natural form of vitamin D that your body makes from sunlight.
Many supplements contain vitamin D as vitamin D2 (calciferol), which is derived from irradiated fungus or made from the fat of lambs' wool. This synthetic variety (often used for fortification of milk and foods) is inferior to the natural form, vitamin D3.
Too much vitamin D can cause an abnormally high blood calcium level, which could result in nausea, constipation, confusion, abnormal heart rhythm, and even kidney stones.
It's nearly impossible to get too much vitamin D from sunlight or from foods (unless you take way too much cod liver oil). Nearly all vitamin D overdoses come from supplements.
The accepted boundary at which vitamin D could become unsafe, is 4,000 IU/day for adults, but recent studies suggest that healthy adults can tolerate more than 10,000 IU of vitamin D per day. The only published vitamin D toxicity was at levels exceeding 40,000 IU/day.
Remember that sunblock!