Goodbye Summer, Goodbye Vitamin D

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The familiar chill of fall reminds us that we're seeing less of the sun. Less sunlight means fewer opportunities to maintain adequate levels of vitamin D in our bodies. With all the buzz surrounding calcium, the importance of vitamin D in supporting strong teeth and bones was long overlooked. So let's spend a few minutes getting up to speed on calcium's biggest supporter, vitamin D.

Vitamin D is a fat-soluble vitamin that is naturally present in few foods, fortified in few others, and available as a dietary supplement. Additionally, our bodies can synthesize vitamin D with adequate sun exposure. The process begins with the inactive form of vitamin D in our skin. When met with sufficient sunlight, the hormone is converted into an active form of vitamin D through a process in our kidneys and liver. Active vitamin D allows our bodies to better utilize calcium, meanwhile playing an important role in maintaining muscle. Thus, vitamin D has been credited with the prevention of falls and subsequent fractures in aging populations.

Groups at higher risk of vitamin D deficiency include older adults, people with limited sun exposure (which would include most Americans in the winter months), people with dark skin, obese individuals, and breastfed infants. So how much do you need? The jury is still out on this one. Current recommendations suggest the following daily intake_

- Age 50 and under: 200 International Units (IU) or 5 micrograms (mcg) - 51-70: 400 IU (10 mcg) - 71 and older: 600 IU (15 mcg)

That said, research suggests these intakes are too low, with some researchers estimating as high as 1000 IU per day. In other words, it's best to think of the current recommendations as minimums.

Below is a list of food sources of vitamin D. As you can see, foods that naturally contain vitamin D aren't common in the American diet, and those that are fortified with vitamin D (most notable being milk) are not very rich sources. So unless you typically consume a tablespoon of cod liver oil daily, or drink upwards of 48 ounces of milk, it's best to leave it to supplementation.

Sources of vitamin D:

Food IUs per serving
Cod liver oil, 1 tablespoon 1,360
Mushrooms, enriched with vitamin D, 3 ounces 400
Salmon, cooked, 3.5 ounces 360
Mackerel, cooked, 3.5 ounces 345
Tuna fish, canned in oil, 3 ounces 200
Orange juice fortified with vitamin D, 1 cup (check product labels, as amount of added vitamin D varies) 142
Milk, nonfat, reduced fat, and whole, vitamin D-fortified, 1 cup 98
Yogurt, fortified with 20% of the DV for vitamin D, 6 ounces (more heavily fortified yogurts provide more of the DV) 80
Margarine, fortified, 1 tablespoon 60
Ready-to-eat cereal, fortified with 10% of the DV for vitamin D, 0.75-1 cup (more heavily fortified cereals might provide more of the DV) 40
Egg, 1 whole (vitamin D is found in yolk) 20
Liver, beef, cooked, 3.5 ounces 15
Cheese, Swiss, 1 ounce 12

For more information, check out the National Institutes of Health Office of Dietary Supplements website.

Tanya Zuckerbrot, MS, RD is a nutritionist and founder of

. She is also the creator of The F-Factor DietaC/, an innovative nutritional program she has used for more than ten years to provide hundreds of her clients with all the tools they need to achieve easy weight loss and maintenance, improved health and well-being. For more information log onto