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Vitamin D Linked to Lower Diabetes Risk . Again
7/25/2011
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Higher intakes or blood levels of the “sunshine-and-seafood” vitamin may help prevent diabetes … judging by the results of a new evidence review from Tufts University.
 
Recent years have seen growing evidence that vitamin D plays a role in the prevention of both kinds of diabetes – childhood (type 1) and adult-onset (type 2).
 
See our sidebar, “Does vitamin D deter diabetes?” to learn what’s been gleaned from the research conducted to date.
 
Sadly, the term “adult-onset diabetes” is no longer accurate, because this form of the disease –caused by poor diets and sedentary lifestyles – is increasingly diagnosed in teens and older children.
 
Does vitamin D deter diabetes?
The answer may be “yes”, in light of the growing body of research that links the two.
 
We cannot yet be certain, because most of the evidence is epidemiological, which cannot prove a cause-and-effect relationship between intakes or body levels of a given food or nutrient and rates of a given disease.
 
The authors of a recent evidence review detailed the current state of the evidence, from epidemiological and clinical studies (Pittas AG et al. 2010):

Vitamin D supplementation in pregnancy or early childhood is associated with a reduced risk of type 1 diabetes.

Most but not all studies link low vitamin D levels to a higher risk of type 2 diabetes.

Clinical trials testing vitamin D supplementation suggest that it may delay the progression to diabetes among adults diagnosed with insulin resistance.
 
The available clinical trials found that vitamin D supplements have no effect on blood sugar levels in healthy adults … which seems both unsurprising and desirable.
 
We should note that people with higher intakes and/or blood levels of vitamin D are generally healthier than their peers, so the positive results reported in some studies might be misleading.
 
For some of our past coverage, see:

And very recent findings reveal that some lean-looking people are at higher risk for diabetes than previously presumed … because they carry a gene (IRS1) that accumulates “visceral” fat around internal organs and yields poor blood sugar and cholesterol profiles (Kilpeläinen TO et al. 2011).
 
Now, a study from Tufts University Medical Center and Carney Hospital in Boston lends weight to the positive end of the evidentiary scale.
 
Review links higher D intakes and blood levels to reduced diabetes risk
The Tufts/Carney team performed a statistical merge (“meta-analysis”) to draw general conclusions from 19 diverse research projects (Mitri J et al. 2011).
 
All 19 reports – eight epidemiological studies and 11 randomized, controlled clinical trials – collected information on people’s vitamin D intake or blood levels and health status.
 
The Boston group’s review produced two important conclusions:
Dietary intakes of vitamin D above 500 IU per day were linked to a 13 percent cut in the risk of diabetes.
Compared to those with vitamin D levels below 14 nanograms per milliliter (ng/mL), people with blood levels above 25 ng/mL were 43 percent less likely to develop diabetes.
 
These apparent links between insufficient vitamin D and diabetes are certainly plausible, since the hormone-like nutrient exerts beneficial effects on risk factors such as pancreatic function, insulin regulation, and inflammation.
 
And, low blood levels of vitamin D have been linked to impaired insulin production and to insulin resistance – a metabolic dysfunction that promotes and characterizes diabetes – in healthy people.
 
How much is enough?
Until recently, most U.S. and global public health agencies thought that a blood level of 20 ng/mL or more was sufficient to support overall good health.
 
But leading academic researchers worldwide now consider 20 ng/mL too low. Many vitamin D testing laboratories have raised their definition of a “normal” blood level to 30 ng/mL or more.
 
And Boston University’s Michael Holick, Ph.D., M.D. – a leading researcher and author of The Vitamin D Solution – echoes most of his peers in pinpointing the optimal level at 40 to 60 ng/mL.
 
Dr. Holick and other experts say that it takes 3,000 IU per day of dietary vitamin D to achieve and maintain that range.
Supplements are the easiest and richest source of vitamin D, but fatty fish come in a close second.
 

Fish fit the vitamin D bill; Sockeye salmon stand out

In addition to getting vitamin D from supplements, certain fish rank among the very few substantial food sources of vitamin D, far outranking milk and other D-fortified foods.

 

 

Among fish, wild Sockeye Salmon may be the richest source of all, with a single 3.5 ounce serving surpassing the US RDA of 400 IU by about 70 percent. Why? See “Why Does Sockeye Offer a Surfeit of Vitamin D?”:

 

Vitamin D per 3.5 ounce serving*

Sockeye Salmon  687 IU

Albacore Tuna  544 IU

Silver Salmon  430 IU

King Salmon  236 IU

Sardines  222 IU

Sablefish  169 IU

Halibut  162 IU

 

*For our full test results, click here.

 
 
Sources
  • Kilpeläinen TO, Zillikens MC, Stančákova A, et al. Genetic variation near IRS1 associates with reduced adiposity and an impaired metabolic profile. Nat Genet. 2011 Jun 26. doi: 10.1038/ng.866. [Epub ahead of print]
  • Mitri J, Muraru MD, Pittas AG. Vitamin D and type 2 diabetes: a systematic review. Eur J Clin Nutr. 2011 Jul 6. doi: 10.1038/ejcn.2011.118. [Epub ahead of print]
  • Pittas AG, Dawson-Hughes B. Vitamin D and diabetes. J Steroid Biochem Mol Biol. 2010 Jul;121(1-2):425-9. Epub 2010 Mar 18. Review.
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