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.
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.
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.