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Vitamin D News: Diabetes, Women’s Health, and Another Reason to Raise the RDA
12/17/2007
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“Sunshine and Seafood” vitamin continues run of good news: Great preventive potential goes largely unrealized due to America’s “D” deficiency

by Craig Weatherby


The body makes vitamin D when sunrays hit bare skin, with lighter skin absorbing more D-making rays, and darker skin accepting less due to UV-blocking pigment.


Wild Alaskan Salmon is the richest food source of vitamin D, by far, with a 3.5 oz serving of Sockeyethe kind of wild Salmon richest in vitamin Dproviding almost seven times more than D-fortified milk, which is the average American’s primary food source (There are 687 IU of vitamin D in a 3.5 oz serving of Sockeye Salmon, but only 100 IU in 8 ounces of milk).


Key Points

  • Finns findings link higher levels of vitamin D to reduced diabetes risk.
  • Germans connect lower levels of vitamin D to breast cancer danger.
  • African-American women need vitamin D far above the current RDA.

Vitamin D deficiency can lead to general ill health, and even the average American blood levelwhich was considered ample until recentlyhas been linked to an increased risk of certain cancers, cardiovascular disease, diabetes, and osteoporosis.


Higher vitamin D levels linked to lower diabetes risk

The idea that vitamin D reduces the risk of type 2 diabetes enjoys considerable evidentiary support, which falls short of conclusive but demands further research.


Like diabetes itself, vitamin D deficiency correlates with impaired beta-cell function and insulin resistancetwo hallmarks of diabetes diagnosesin animal and human studies.


Results of a 17-year epidemiologic studythe type which follows a group’s diet and health status over time—show that people with the highest blood levels of vitamin D were the least likely to develop diabetes, and vice versa


The Finnish study began in 1978 and involved 4,423 men and women aged 40 to 69.


Researchers collected blood samples and information on the participants’ lifestyle habits, diets, health status, and prescriptions.


During 17 years of follow-up, the risk among those with the highest blood levels of vitamin D was 40 percent lower compared to the participants with the lowest blood levels.


The risk was calculated after adjusting for age and sex and accounting for the season when each volunteer’s blood was drawn (The seasonal adjustment was necessary because the body makes vitamin D in response to sun exposure).


The researchers noted that in their study, the reduced diabetes risk associated with higher D intake fit with findings that higher intake of fishwhich of course, are also high in beneficial omega-3sreduces the risk of cardiovascular disease.


Who can argue with their final conclusion? “Further research is needed to confirm the association and to distinguish between the independent role of vitamin D and the role of healthy dietary and lifestyle patterns in reducing the risk of type 2 diabetes” (Mattila C et al 2007).


Amen.


Lower vitamin D levels linked to higher breast cancer rates

Last June, we reported on a large epidemiological study by a Harvard team, which linked higher vitamin D intake to lower risk of breast cancer.


Among the pre-menopausal participants, higher calcium and vitamin D intake were associated with 39 and 35 percent lower risks of breast cancer, respectively. No risk reductions were found among post-menopausal participants (See “Vitamin D + Calcium May Cut Pre-Menopause Breast Risks”).


The very same month, the authors of a randomized controlled trial found a 60 percent reduction in internal cancers in women taking 1,100 IU per day of vitamin D: an amount almost triple the absurdly low US RDA (400 IU). The researchers came to a clear conclusion: “Improving calcium and vitamin D nutritional status substantially reduces all-cancer risk in postmenopausal women” (Lappe JM, et al 2007).


Now, a large epidemiological study on breast cancer found that women with breast cancer were three times more likely to have low vitamin D levels.


In the new German study, 1,394 women with breast cancer were compared with a similar number of women without breast cancer.


As they wrote, “Our findings strongly suggest a protective effect for postmenopausal breast cancer through a better vitamin D supply… with a stronger inverse association in women with low [vitamin D] concentrations (< 50 nmol/L)” (Abbas S et al 2007).


In other words, the risks associated with lower vitamin D blood levels were greater than the protection associated with higher levels.


The problem is that most of Americans don’t get near enough D from sun exposure to make up for the paltry amounts in our diets.


And darker skinned people are at the greatest disadvantage, unless they get ample amounts from supplements, or better yet, from wild Salmon,which is rich in omega-3s and D alike.


Study in darker skinned women fuels fight to raise the RDA for Vitamin D

Results of a three year study in 208 post-menopausal African-American women indicated that they need 2,000 International Units (IU) of vitamin D3 to ensure adequate blood levels of the vitamin (Talwar SA et al 2007).


This is four times the current US RDA, and 2,000 IU is also the current safe upper intake level (UL) approved in the US.


The findings add to a growing body of evidence that’s led many researchers to urge an urgent increase in the current RDA for vitamin D, from 400 IU to 2,000 IU.


Increased skin pigmentation reduces the amount of UVB radiation absorbed in skin, so that darker skinned Americans are more at risk of vitamin D deficiency.


As we've noted, blood levels officially considered normal and adequate50 nanomoles per liter (nmol/L)have been linked to increased risk of common diseases.


But most vitamin D research indicates that we need blood levels of 80 to 100 nmol/Lor about double the American averagefor optimal health.


Researchers from Winthrop University Hospital, Mineola, New York assigned half the 208 women to take 800 IU of vitamin D3 for two years, and 2,000 IU for a third and final year.


The authors reported that the lower dose raised vitamin D levels from an average of 47 nmol/L to 71.4 nmol/L after three months. After three months at the higher dose (2,000 IU), the average blood level was an optimally healthful 87 nmol/L.


More than 90 percent of the participants achieved a blood level above 50 nmol/L, while 60 percent attained levels greater than 75 nmol/L.


As the authors wrote, “Supplementation with 2000 IU/day… is sufficient to raise [vitamin D blood] concentrations to greater than 50 nmol/L in almost all postmenopausal African American women.… higher doses were needed to achieve concentrations greater than 75 nmol/L in many women in this population.”


The authors of a recent evidence review reported that the safe upper intake level for oral vitamin D3 should be increased five-fold, to 10,000 IU per day (see “Review Supports Safety of Much Higher Vitamin D Intake”).



Sources

  • Abbas S, Linseisen J, Slanger T, Kropp S, Mutschelknauss E, Flesch-Janys D, Chang-Claude J. Serum 25-hydroxyvitamin D and risk of postmenopausal breast cancer - results of a large case-control study. Carcinogenesis. 2007 Oct 31; [Epub ahead of print]
  • Aloia JF, Talwar SA, Pollack S, Feuerman M, Yeh JK. Optimal vitamin D status and serum parathyroid hormone concentrations in African American women. Am J Clin Nutr. 2006 Sep;84(3):602-9.
  • Lappe JM, et al. Vitamin D and calcium supplementation reduces cancer risk: results of a randomized trial. Am J Clin Nutr. 2007 Jun;85(6):1586-91.
  • Lin J, Manson JE, Lee IM, Cook NR, Buring JE, Zhang SM. Intakes of calcium and vitamin d and breast cancer risk in women. Arch Intern Med. 2007 May 28;167(10):1050-9.
  • Mattila C, Knekt P, Männistö S, Rissanen H, Laaksonen MA, Montonen J, Reunanen A. Serum 25-hydroxyvitamin D concentration and subsequent risk of type 2 diabetes. Diabetes Care. 2007 Oct;30(10):2569-70. Epub 2007 Jul 12.
  • Rauscher M. Vitamin D may curb type 2 diabetes risk. Reuters Health. November 19, 2007. Accessed online December 16, 2007 at http://www.nlm.nih.gov/medlineplus/news/fullstory_57762.html.
  • Talwar SA, Aloia JF, Pollack S, Yeh JK. Dose response to vitamin D supplementation among postmenopausal African American women. Am J Clin Nutr. 2007 Dec;86(6):1657-62.

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