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Most of us know that vitamin D works with calcium to grow strong bones and to prevent osteoporosis. However, researchers have found that vitamin D has additional important effects on the body. Studies have shown that adequate circulating levels of vitamin D may decrease risk for developing heart disease, cerebrovascular disease, diabetes, cancer and/or falls.
Adequate vitamin D and its receptors (VDR’s) in skeletal muscle promote growth of muscle proteins, enhancing strength and function. A drop in vitamin D levels causes protein breakdown and loss of muscle fibers, known as sarcopenia. Vitamin D deficiency also reduces energy production for muscle contraction. Taken together, these effects cause muscles to weaken, affect walking ability and balance, and increase risk for falls. Conversely, researchers have found that individuals with high circulating levels of vitamin D experience fewer falls than those with low levels of this nutrient.
Vitamin D appears to have a protective effect against certain types of cancers, especially colon and colorectal cancers, by regulating cell cycles and causing cancer cell death. There is mixed evidence that vitamin D reduces breast cancer risk. More research is needed to clarify this effect.
Cardiovascular and cerebrovascular diseases have been linked to chronic inflammation and production of cellular proteins called cytokines. Adequate vitamin D levels suppress cytokine production and decrease inflammation. Additionally, high vitamin D levels and VDR’s in the heart and blood vessels are associated with low risk of heart attack. There is strong evidence that good vitamin D status reduces the risk for stroke.
Vitamin D is acquired through two main sources: 1) consumption of vitamin D-rich foods and supplements and 2) production of vitamin D in the skin when it is exposed to ultraviolet light from the sun. Foods highest in vitamin D are fish such as cod, salmon, tuna and mackerel. Meats are next, followed by foods fortified with vitamin D, such as orange juice, yogurt, margarine, cereal.
Surprisingly, most adults and older adults in industrialized nations are deficient in vitamin D, and this trend continues to grow. Reasons include decreased exposure to sunlight, attributed to time spent indoors and increased use of sunscreen, and reduced consumption of vitamin D-rich foods. Vitamin D status declines with age due to reduced dietary consumption and intestinal absorption, decreases in skin conversion and losses in kidney function. So the time to work on your vitamin D status is now!
There is disagreement among government health agencies regarding the recommended daily allowance for vitamin D. The Institute of Medicine recommends daily consumption of 400 IU for individuals aged 51-70 years and 600 IU for those older than 70 years. However, recent studies demonstrated that higher doses appeared more effective (e.g., 1000-2000 IU).
Be sure to talk with your physician prior to purchasing any supplements. He or she can do a blood test to determine your vitamin D levels, and then prescribe the amount of this nutrient that is appropriate for you.
Constance McCloy, PT, EdD
Associate Professor
References:
Kikkinen A et al. Vitamin D status and the risk of cardiovascular disease death. American Journal of Epidemiology. 2009;170:1032-1039.
National Institutes of Health Dietary Supplement Factsheet: Vitamin D. http://ods.od.nih.gov/factsheets/vitamind.asp Retrieved July 19, 2010.
Ruxton CH and Derbyshire E. Health impacts of vitamin D: are we getting enough? British Nutrition Foundation Nutrition Bulletin. 2009;34:185-197.
Schact E and Richy F. Reduction of falls in elderly: the central role of alfacalcidol in a multi-dimensional paradigm. Internet Journal of Epidemiology. 2009;7:1-14.
Zhou G, Stoitzfus J, Swan B. Optimizing vitamin D status to reduce colorectal cancer risk: an evidentiary review. Clinical Journal of Oncology Nursing. 2009;13:E3-E17.
5 Comments:
I'm reading more and more that it's super important to get vitamin d early in life and that getting it from the sun is best. I have my children outside without sunscreen as often as I can. Here is a related article that talks about getting it early in life to prevent bone weakness... http://biovedawellness.com/2010/07/early-supplementation-of-vitamin-d-and-calcium-shown-to-reduce-osteoporosis-risk/
Thanks for your comment Jennifer and I will check out the website you referred us to. RE: getting kids out in the sunshine: I would imagine there are many factors to take into consideration re: amount of time in sun and time of day (exposure to UV rays) that is optimal for your children. Their skin type would also come into play. I'm wondering if your physician might have some nationally published guidelines that would be of assistance to you to figure out what's healthiest for your kids re: sun exposure time.
A recent review of 45 vitamin D studies conducted by the Cochrane Collaboration Vitamin D and vitamin D analogues for preventing fractures associated with involutional and post-menopausal osteoporosis.
"Overall there is a small but significant increase in gastrointestinal symptoms and renal disease associated with vitamin D or its analogues. "
None of the healthy controls in the NCI cancer study had vitamin D concentrations over 31.25 ng/ml .
Vieth and like minded researchers all sound very plausible but what they consider to be a optimal vitamin D level is naturally attained by virtually nobody apart from a minority of Hawiian lifeguards. By nobody I don't just mean in the US, I mean nobody on earth. People whose evolution has been in tropical regions of the world have adapted to the year round intense sunlight they are exposed to and it is clear that involves having low vitamin D levels. For example a review of vitamin D in Africa (Here) gives the median levels of 26 ng/ml for the equatorial countries Kenya and Congo. There is now solid evidence to support the idea of this genetic tendency to low vitamin D levels in those of tropical ancestry. Blood vitamin D levels in relation to genetic estimation of African ancestry
"The effect of high vitamin D exposure from sunlight and diet was 46% lower among African Americans with high African ancestry than among those with low/medium ancestry. Conclusions: We found novel evidence that the level of African ancestry may play a role in clinical vitamin D status"
I'm sure other populations which evolved in intense sunlight are much the same. In a study from south India,” (High prevalence of vitamin D deficiency in healthy south Indians) levels below 20ng/ml were found in 44% of the men and 70% of the women yet they got a lot of sun. The subjects are described as “agricultural workers starting their day at 0800 and working outdoors until 1700 with their face, chest, back, legs, arms, and forearms exposed to sunlight"
In (Hollis et al 2007) even "Honolulu, Hawaii volunteers with a self-reported sun exposure time of three or more hours per day on five or more days per week for at least the preceding three months exhibited a wide range of circulating circulating vitamin D levels (11–71 ng/mL).
I don't understand why anyone would think levels of D found in a minority of surfers with massive sun exposure (year round UV exposure that no ancestral European ever got ) is perfect. Most subjects never got near 60 ng/ml and that is clearly not due to lack of sun, ithe majority of people are naturally selected NOT to reach double the average of normal healthy people (31ng/m l ) by sun exposure. For example "Europeans are genetically polymorphic in their ability to maintain blood levels of vitamin D. At least two alleles reduce the effectiveness of the vitamin-D binding protein, and their homozygotes account for 9% and 18% of French Canadians (Sinotte et al., 2009)". (Sinotte et al 2009)
Hollis (2007 investigated two separate populations: the first, (discussed above) individuals from Hawaii who received significant sun exposure; the second, subjects from a lactation study who received up to 6,400 IU vitamin D3/day for six months. "the range of circulating 25(OH)D levels in women in the supplementation group was from 12–77 ng/mL"
Yikes! they went higher than the extremely sun exposed Hawaii subjects on a mere 6,400 IU. What is even more worrying is that many did not; if they were trying to attain the perfect level of 60ng/ml these women would indeed have to take 10,000 IU. Where is the harm in that ? Well, ingested vitamin D is not the same as skin synthesised D Human plasma transport of vitamin D after its endogenous synthesis says
"These findings indicate that endogenously synthesized vitamin D3 travels in plasma almost exclusively on DBP, providing for a slower hepatic delivery of the vitamin D and the more sustained increase in plasma 25-hydroxycholecalciferol observed after depot, parenteral administration of vitamin D. In contrast, the association of orally administered vitamin D with chylomicrons and lipoproteins allows for receptor-mediated, rapid hepatic delivery of vitamin D, and the reported rapid but less-sustained increases in plasma 25-hydroxycholecalciferol".
So supplementation is not handled in the same way; ingestion of vitamin D is not really the same. Is there any reason to think 10,000IU of D sloshing through the circulation will do harm ? Yes. Vitamin D and osteogenic differentiation in the artery wall
"There is some evidence to suggest that dietary vitamin D may be carried by lipoprotein particles into cells of the artery wall and atherosclerotic plaque, where it may be converted to active form by monocyte-macrophages. These findings raise interesting questions regarding the effects of vitamin D intake on atherosclerotic calcification and cardiovascular risk.”
Since that was written Vitamin D, Adiposity, and Calcified Atherosclerotic Plaque in African-Americanshas demonstrated positive associations between 25-hydroxyvitamin D and aorta and carotid artery CP in African-Americans.
Great post! Vitamin D-rich dairy sources go beyond yogurt. Dairy foods are the main source of calcium and vitamin D in the diets of Americans (Keast, D.R., S.L. Hoerr, V.L. Fulgoni, et al. FASEB J. V19(4): A59 (abst. # 62.5), 2005) and nearly all milk in the U.S. is fortified with vitamin D. Three 8-oz. glasses of low-fat or fat-free, vitamin D-fortified milk or equivalent milk products daily, as recommended by the 2005 Dietary Guidelines for Americans ages 9 years and older, provide 90 percent of the recommended Daily Value (DV) for calcium and 75 percent of the DV for vitamin D. Additionally, some cheeses also are fortified with vitamin D, so it’s important for consumers to be encouraged to read nutrition labels on these products.
Also two different studies presented at the Experimental Biology meeting in April found dairy foods were not only the top contributing food category of calcium (providing 38.6 percent contribution to overall intake) and vitamin D (52.3 percent), but also the second- and third-highest sources for phosphorus and potassium, respectively. In addition, dairy foods were found to be the top contributors of vitamin D in the diets of children 2-18 years old (68.1 percent contribution to overall intake) and adults 19 years and older (46 percent).
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