Strictly speaking, vitamin D isn’t a vitamin at all. It’s more of a hormone, produced in skin cells exposed to UVB rays of sunlight. The form that’s produced in skin cells is metabolized to an active form by the liver and kidneys.
Not just for bones
You might know that vitamin D is critical for calcium absorption and bone health. It’s also important for immune, brain, heart, and muscle function. There’s emerging evidence that vitamin D is important for skin health and integrity: vitamin D is produced in the skin, and activated vitamin D then helps keep skin healthy.
Our anti-vitamin D lifestyle
Early humans didn’t worry about vitamin D. Sun exposure was part of daily life. Modern life is the polar opposite. We spend most of our waking hours inside, whether in buildings or cars. Thanks to a link with skin cancer, people are terrified of sun exposure. If we venture outside, we’re slathered in sunscreen or covered in clothes. No opportunity for vitamin D production in skin. Vitamin D status is negatively impacted by:
- indoor lifestyle
- no skin exposed to sunlight
- winter (shorter days and weaker sunlight)
- living at northern latitudes
- darker toned skin
- poor absorption (age, digestive dysfunction)
- poor intake
- avoidance of dairy products
The first 6 problems are all related to skin exposure to adequate sunlight to promote vitamin D production. Aging can lead to 3 additional barriers to vitamin D.
- Reduced appetite or digestive dysfunction can lead to lower intake of vitamin D-fortified foods like milk.
- Vitamin D production in skin, even with sufficient sun exposure, falls off with aging.
- Even if intake appears adequate, absorption can be impaired by intestinal dysfunction, poor diet or medications.
Obesity can impact vitamin D status regardless of age or sun exposure. Why? Vitamin D is a fat soluble vitamin. Fat is like a vitamin D magnet: excess body fat can sequester vitamin D in fat cells, pulling it out of circulation so it isn’t available to all the body tissues that need it.
What to do?
First, don’t assume you need a supplement. Your blood level might be sufficient. A simple blood test can give you that information. If your level is insufficient or deficient, you need to take steps.
Boosting sun exposure is problematic for many people, thanks to worries about the damaging effects of UV rays. Increased sun exposure might not even be meaningful in many locations. For example, from November to March, the UVB rays needed to produce vitamin D are absent above latitude 40º north (New York City, Rome, Tokyo, and Salt Lake City are approximately along this latitude).
Alternatives to sunshine for your vitamin D
Boosting intake is a good way to support your vitamin D status all year long, regardless of sun exposure. You can get vitamin D from diet, but sources are limited. Fatty fish — such as salmon, mackerel, sardines — has some. Egg yolk is another source (and to think we’ve been told to avoid egg yolks all these years!). Dairy products fortified with vitamin D are one of the most reliable sources: milk, foods made with milk (smoothies, pudding, soups, milk shakes, etc), yogurt or cheese fortified with D and foods made with cheese or yogurt. Some convenience foods and ready-to-eat cereals are also fortified with vitamin D.
There’s a catch. Vitamin D is fat soluble, as noted above. You need to consume D with a meal that includes fat to enhance absorption. The vitamin D in your cereal might be poorly absorbed if you eat your cereal with skim (non-fat) milk.
What about supplements? The vitamin D3 form (cholecalciferol) is better absorbed. Find it in gel capsules (see photo). If you do opt for a supplement, the same rules of absorption apply. Take your supplement with a meal that includes fat. Don’t take it on an empty stomach.
Some people swear by cod liver oil, one of the original vitamin D supplements. One tablespoon has roughly twice the recommended daily intake for an adult. The catch is that cod liver oil is very high in the active form of vitamin A, which can be toxic at high intake levels.
How much supplemental vitamin D? If you’ve had a blood test, your physician can offer advice on a dose, depending on your test results. You can buy vitamin D gel caps. Or rely on the D included with other supplements you may take, such as calcium or a multiple.