Does vitamin D deficiency drive people's risk for diabetes higher?
The answer may be yes, based on the results of a new Spanish study.
They support earlier signs that vitamin D may help prevent or ease the disease.
Epidemiological studies indicate a clear correlation between vitamin D deficiency and a higher risk for type 1 and type 2 diabetes.
Fish fit the vitamin D bill; Sockeye salmon stand out
offer an easy way to get ample doses of vitamin D.
But whole foods are the best source ... and certain fatty fish abound in vitamin D, far outranking milk and other D-fortified foods.
Wild sockeye salmon
ranks as the richest source, with a single 3.5-oz. serving surpassing the US RDA of 600 IU by about 15 percent:
IUs of Vitamin D
per 3.5-oz. serving*
Sockeye salmon 687
Albacore tuna 544
Silver salmon 430
King salmon 236
Vitamin D deficiency also predisposes lab animals to both types of diabetes, while high doses of vitamin D prevent the disease.
And sun exposure itself, in addition to dietary vitamin D, seems to exert some diabetes-preventive effects (Shore-Lorenti C et al. 2014).
We still lack hard evidence from large, well-designed clinical trials … which have so far produced mixed results (Seida JC et al. 2014).
But the results of a new study support the very plausible hypothesis that vitamin D plays a big role in blood-sugar control.
Spanish study links low vitamin D levels to diabetes
The authors of the new study compared vitamin D levels in healthy and diabetic people, and in obese and non-obese people (Clemente-Postigo M et al. 2015).
Their results suggest that people with low vitamin D levels are more likely to have diabetes, regardless of how much they weigh.
Previous studies suggested that people with low vitamin D levels are more likely to be obese and to have type 2 diabetes, pre-diabetes, and metabolic syndrome.
"The major strength of this study is that it compares vitamin D levels in people at a wide range of weights (from lean to morbidly obese) while taking whether they had diabetes into account,” said lead author Mercedes Clemente-Postigo, from Spain's University of Malaga.
Her team found that the participants' vitamin D levels directly correlated with blood sugar (glucose) levels, but not with their body mass indices (BMIs).
As they wrote, "[This suggests] that vitamin D deficiency is associated more with carbohydrate metabolism than with obesity.”
How much "D” do we need?
First things first: which form of vitamin D is best?
Vitamin D3 is the "natural” form created when sunrays hit human skin.
Otherwise, it's abundant only in fatty fishy such as wild salmon … see our sidebar, "Fish fit the vitamin D bill”.
The body uses D3 more readily than D2, and D3 is more potent than D2 for producing the "storage” form of vitamin D (25-hydroxyvitamin D), which fulfills the body's vitamin D functions.
Currently, the Institute of Medicine recommends maintaining a vitamin D blood level of 20 to 50 ng/mL.
But many experts in the field urge people to maintain a blood level of 30 to 100 ng/mL to achieve true vitamin D "sufficiency” … a conclusion embodied in the Endocrine Society's 2011 clinical practice guidelines (Holick MF et al. 2011; Heaney RP et al. 2011).
If a doctor tests your vitamin D levels, make sure he or she orders a 25-hydroxyvitamin D test. And many doctors consider a result of 30 ng/mL (75 nmol/L) as "sufficient”, so ask to see yours.
The Endocrine Society currently recommends the following vitamin D intakes, preferable vitamin D3 (Holick MF et al. 2011):
Age 0 to 1 year - 400 to 1,000 IU/day
Age 1 to 18 years - 600 to 1,000 IU/day
All adults over age 18 - 1,500 to 2,000 IU/day
Pregnant or nursing women under age 18 - 600 to 1,000 IU/day
Pregnant or nursing women over age 18 - 1,500 to 2,000 IU/day
There's also general agreement among expert researchers that vitamin D intakes of up to 4,000 IU per day are safe.
However, when it raised the vitamin D RDAs in 2010, the IOM only raised the upper intake limit to 2,000 IU.
Frankly, we rely more on advice from the vitamin D and hormone experts at the Endocrine Society, but you must make your own judgment.
Beto JA. The role of calcium in human aging. Clin Nutr Res. 2015 Jan;4(1):1-8. doi: 10.7762/cnr.2015.4.1.1. Epub 2015 Jan 16. Review.
Clemente-Postigo M et al. Serum 25-Hydroxyvitamin D and Adipose Tissue Vitamin D Receptor Gene Expression: Relationship With Obesity and Type 2 Diabetes. J Clin Endocrinol Metab. 2015 Feb 23:jc20143016. [Epub ahead of print]
Kampmann U, Mosekilde L, Juhl C, Moller N, Christensen B, Rejnmark L, Wamberg L, Orskov L. Effects of 12 weeks high dose vitamin D3 treatment on insulin sensitivity, beta cell function, and metabolic markers in patients with type 2 diabetes and vitamin D insufficiency - a double-blind, randomized, placebo-controlled trial. Metabolism. 2014 Sep;63(9):1115-24. doi: 10.1016/j.metabol.2014.06.008. Epub 2014 Jun 19.
Mousa A, Naderpoor N, Teede HJ, de Courten MP, Scragg R, de Courten B. Vitamin D and Cardiometabolic Risk Factors and Diseases. Minerva Endocrinol. 2015 Feb 25. [Epub ahead of print]
Seida JC, Mitri J, Colmers IN, Majumdar SR, Davidson MB, Edwards AL, Hanley DA, Pittas AG, Tjosvold L, Johnson JA. Clinical review: Effect of vitamin D3 supplementation on improving glucose homeostasis and preventing diabetes: a systematic review and meta-analysis. J Clin Endocrinol Metab. 2014 Oct;99(10):3551-60. doi: 10.1210/jc.2014-2136. Epub 2014 Jul 25. Review.
Shore-Lorenti C, Brennan SL, Sanders KM, Neale RE, Lucas RM, Ebeling PR. Shining the light on Sunshine: a systematic review of the influence of sun exposure on type 2 diabetes mellitus-related outcomes. Clin Endocrinol (Oxf). 2014 Dec;81(6):799-811. doi: 10.1111/cen.12567. Epub 2014 Sep 9.