Nutrition Q: do I have to take a vitamin D supplement?
Nutrition Q: do I have to take a vitamin D supplement?
A: in short, it is often quite helpful to take a vitamin D supplement, and this is coming from a very much team “food first” dietitian. Vitamin D, which helps the body absorb calcium and promotes bone strength and growth, is often an exception because it’s only in a select number of foods and can be difficult for the body to produce enough from the sun in certain climates and times of year. In fact, a recent study found as many as 75% of U.S. teens and adults experienced vitamin D insufficiency, which can lead not only to weakened bones and the development of osteoporosis, but may also increase risk for cardiovascular disease and some cancers. For my runner friends, vitamin D insufficiency can also increase risk for stress fractures (no matter how much calcium you’re consuming!).
Needless to say, it’s important to maintain adequate levels of vitamin D. Aside from supplementation, here are the other ways we can help the body get enough:
Vitamin D from the sun
When our skin is exposed to ultraviolet rays from the sun, it triggers a reaction that synthesizes vitamin D. This is often the primary way some individuals maintain adequate vitamin D levels in the body, but the amount of vitamin D your body can make from the sun depends on a few different factors:
The time of day – the body produces the most vitamin D from sun exposure midday, when the sun is at a particular angle that makes its rays the strongest
Where you live – in regions close to the equator, it’s easier to produce vitamin D from sun exposure throughout the year. A good indicator of whether or not you are receiving adequate sun exposure to make vitamin D is to take a look at your shadow. If it's longer than you are tall, you’re not making much vitamin D
Skin color – pale skin makes vitamin D more quickly, in as little as 15 minutes, and darker skin may take an hour or more
The amount of skin you expose - the more skin you expose, the more vitamin D the body may make. However, sunscreen blocks much of this production, and it's best to speak with your dermatologist to determine what level of sun exposure is safe for you
Vitamin D food sources
Vitamin D is not present in a ton of foods, and most vitamin D-containing foods are animal products:
Cod liver oil
Swordfish
Salmon
Tuna
Fortified orange juice, cereals and milk
Sardines
Liver
Eggs (yolk)
When to supplement
While it’s possible for the body to make enough vitamin D from the sun and to obtain it from food sources, it’s more common to need a supplement. Especially if you’re vegan, vegetarian, or simply don’t like much of the foods I listed above, and if you don’t receive adequate sun exposure (hello, winders in the northeast!). I usually recommend having vitamin D levels checked a few times per year since they can change with the seasons and level of sun exposure you’re getting, and supplementing as needed. Working with your dietitian or doctor on supplementation dosage is helpful, as individual needs may differ.
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