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As Daylight Hours Decrease, So Does Vitamin D Absorption

By Michael R. Williams, RD

Soon the spring and summer sun will be replaced by the long dark, days of autumn. For most of us, this transition to the cooler climate means less time outside. These shorter days, decreased sunshine and more time indoors is a particularly problematic recipe for Western New Yorkers when it comes to vitamin D.

Vitamin D is a unique nutrient as it is produced by the skin when exposed to sunlight. For most people, it takes about 10-15 minutes of sun exposure to the arms and legs a few times a week to meet the body’s needs. Unfortunately, the sun rays that reach Western New York during autumn, winter and early spring are not strong enough for adequate absorption. Relying only on the sun during these months may give way to a vitamin D deficiency.

Vitamin D deficiency, an all too common condition, can lead to some nasty consequences. First and foremost, the main function of vitamin D is the maintenance of calcium balance, which helps to keep our bones and teeth strong. A deficiency quickly increases the risk of many bone disorders like osteoporosis, osteomalacia (adult rickets) and rickets. Moreover, maintaining adequate vitamin D stores has been strongly linked in the prevention of colon, prostate and breast cancer, cardiovascular disease and even diabetes.

To avoid a deficiency, most people need to consume extra vitamin D from foods or supplements. Unfortunately, there are not many great food sources. The best sources are fatty fish including salmon, swordfish and mackerel, which all provide more than 300 IU per serving. Other sources are fortified milks, yogurts and orange juices which have about 100 IU. Comparatively, the Recommended Dietary Allowance for children (1+ years) and adults is 600 IU per day. So unless you eat a lot of fatty fish and drink big glasses of fortified orange juice every single day, you probably aren’t getting enough vitamin D.

Common multivitamins are helpful as they provide around 50 to 400 IU. Even better, a vitamin D supplement can have 1000 to 2000 IU. But be careful of getting too much. The Institute of Medicine has set an Upper Limit level of 4000 IU a day to avoid toxicity (for children under 9 the level is lower).

If you are not eating fatty fish daily or taking a Florida vacation soon, you most likely should take a Vitamin D supplement. But remember there is always too much of a good thing and definitely speak with your healthcare provider before beginning any new supplements.

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