Investing in Nutrient Dense Food: Vitamin D
Dr. Weston A. Price identified three nutrients in his book Nutrition and Physical Degeneration that proved vital to the development and maintenance of healthy teeth. I looked at cost-effective sources of the first of these in Investing in Nutrient Dense Food: Vitamin A, so now it's time to move on to the second, vitamin D.
Like vitamin A, vitamin D isn't a single compound. It's a group of fat soluble compounds that are responsible for enhancing our body's capacity to absorb minerals such as calcium, iron, magnesium, phosphate and zinc, promotes healthy bone growth and protects us against cancer, heart disease and other chronic diseases . While there are other compounds that fall in the group commonly referred to as 'Vitamin D', the two most important are ergocalciferol (vitamin D2) and cholecalciferol (vitamin D3). Cholecalciferol is most commonly synthesized in our skin from cholesterol during exposure to sunlight . In the liver cholecalciferol is converted to a compound called calcidiol, which is then converted to calcitriol, the biologically active form of Vitamin D, in the kidneys.
Unfortunately there aren't many foods that contain meaningful amounts of Vitamin D, and all of them are from either animals or fungi, the latter of which are more closely related to animals than they are to plants. The graph below shows the cost associated with providing a daily allowance of 600 International Units (IU) of vitamin D from several foods, with nutrition data from the USDA's National Nutrient Database and price data gathered at my local farmers' market or grocery cooperative for pasture based livestock and wild-caught fish .
Many sources of health information push seafood as a source of vitamin D, particularly salmon and tuna. While these foods do contain decent amounts of the vitamin, when we figure in their comparatively high cost they don't look particularly cost-effective. Tuna, at $17 per pound at my local grocery cooperative, is an expensive way to get vitamin D, and wild caught salmon is even more so. Sardines were a bit less pricey and pack more vitamin D per unit weight, but in terms of cost-effectiveness still couldn't beat pasture raised eggs. Beef liver and kidneys were also among the most cost-effective sources of vitamin D, which is intriguing as they also top my list of cost-effective sources of vitamin A.
Mushrooms are typically poor sources of vitamin D, as seen by the high cost associated with getting 600 IU's worth from portobello mushrooms, but when freshly picked fungi are exposed to ultraviolet light for at least five minutes their levels of ergocalciferol (vitamin D2) rise dramatically. In the graphic above these irradiated portobellos are marked with an asterisk, and yield D2 at a cost of just over $3 per 600 IU. That's about half the price of the vitamin D in eggs, so if you have access to an ultraviolet light and fresh mushrooms you can take a crack at ultra-fortifying your fresh fungi. It's worth noting though that some question vitamin D2's ability to substitute for vitamin D3 in human metabolism, since most vitamin D produced by humans during sun exposure and used metabolically is D3 . It's not clear that these ultra-fortified mushrooms can make up for lack of vitamin D from other sources.
While some foods are more cost-effective sources of vitamin D than others, none are particularly cheap. I'm not going to speak for anyone else, but it seems to me that the most cost-effective way to get vitamin D is via sun exposure, so that's the route I take. One nice thing about vitamin D is that it's fat soluble, so excess produced during the summer is easily stored in body fat for use over the winter when sun exposure isn't direct enough to stimulate production in the skin. Most sources I've read suggest that 10-20 minutes of direct sun exposure for light complected people during the summer produces up to 10,000 IUs of vitamin D, although those with darker skin or who live in northern latitudes with less direct sun exposure will produce less.
One last note before I leave vitamin D: there remains controversy surrounding how much of this nutrient the human body actually needs. I used a recommended daily allowance of 600 IU, taken from the US Department of Health's website, but some researchers claim the human body is adapted to producing and using upwards of 4,000 IU of vitamin D per day, most of this coming from sun exposure . The difference between 600 IU and 4,000 IU is substantial, and given little evidence that the higher intake levels could be toxic - particularly when achieved via sun exposure, which has inherent feedback mechanisms that prevent the production of toxic levels of vitamin D - it seems prudent to me to up my production of the vitamin. All in all, it's just another good excuse to spend time outside during the summer...
- Vitamin D: Fact Sheet for Consumers. United States Department of Health and Human Services, National Institutes of Health.
- M. Holick (2006) High prevalence of Vitamin D inadequacy and implications for health. Mayo Clinic Proceedings, Vol. 81, Pgs. 353-373.
- National Nutrient Database for Standard Reference. United States Department of Agriculture, Agricultural Research Service.
- L. Houghton & R. Veith (2006) The case against ergocalciferol (Vitamin D2) as a vitamin supplement. The American Journal of Clinical Nutrition, Vol. 84, Pgs. 694-697.
- R. Heaney & M. Holick (2011) Why the IOM recommendations for vitamin D are deficient. Journal of Bone and Mineral Research, Vol. 26, Pgs. 455-457.
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