Vitamin D expert: beware of misleading research

Published: Jan 10, 2014
Author: BioCeuticals - Editor

Practitioners urged to continue maintaining patients’ vitamin D status

World-leading vitamin D expert, Professor Michael F. Holick has called for practitioners to ensure their patients are maintaining good vitamin D status to help reduce the risk of chronic illnesses, following a recent review of vitamin D research that has been misrepresented in media reports.

The review of existing data, published in The Lancet, identified 290 prospective cohort studies and 172 randomised trials of major health outcomes and of physiological parameters related to disease risk or inflammatory status.¹

The authors of Vitamin D status and ill health: a systematic review concluded that a number of randomised trials have not confirmed that raising of 25-hydroxyvitamin D (25[OH]D; used as a proxy for an individual’s vitamin D status) concentrations can modify the occurrence or clinical course of chronic health disorders such as breast and colorectal cancer.¹

However, Prof. Holick, a pioneer in vitamin D research, has claimed the review and the media attention surrounding it misleads readers into believing there is new research.

“To look at these meta-analysis and make conclusions on the health benefits of vitamin D is not appropriate. There is really nothing new in this review and it really does misrepresent some very good studies demonstrating associations of vitamin D and chronic illnesses.”

Prof. Holick, endocrinologist and Professor of Medicine, Physiology and Biophysics at Boston University (USA) said despite the review’s large sample size, the problem with many of the reviewed studies was their use of suboptimal doses of vitamin D.

According to research, to increase serum vitamin D levels to around 50nmol/L (sub-optimal level), normal healthy adults require 1000IU/day of vitamin D.² A dose of 4000IU/day of vitamin D is required to increase serum vitamin D to around 75nmol/L (sufficiency).³

“For example, in the Women’s Health Initiative Calcium/Vitamin D Supplementation Study referred to in the review, researchers gave women only 400IU of vitamin D along with 1000mg calcium. No benefit was found in reducing colorectal or breast cancers.

“The second problem is that often these huge studies are being conducted and at the end they find out there’s a really high non-compliance rate. Sometimes 40%, 50% or even 60% of the subjects are admitting that they didn’t take their vitamin D,” said Prof. Holick.

In fact, of the participants in the Women’s Health Initiative Study who were compliant and actually took the supplementation, on average 14% had a reduced risk of developing cancer. Women who were most vitamin D deficient had a 253% increased risk of developing colorectal cancer over 8 years compared to women who had an initial blood level of 60nmol/L.

Prof. Holick called for practitioners to carefully dissect the treatment methods and results of the vitamin D trials analysed in the review, especially where media fail to read the full papers and rely on the abstract.

When reviewing trials, Prof. Holick recommended looking at whether researchers measure the blood levels at the beginning and at the end of the treatment period, as well as the length of the treatment period.

The authors of Vitamin D status and ill health: a systematic review stated “High 25(OH)D concentrations were not associated with a lower risk of cancer, except colorectal cancer.”

However, in a clinical trial cited in the review, researchers tested 1,179 postmenopausal women residing in rural Nebraska and found that subjects supplemented daily with calcium (1,400–1,500 mg) and vitamin D3 (1100 IU) had a significantly lower incidence of cancer over 4 years compared with women taking a placebo. Women taking 1100IU/day of vitamin D had a reduced risk of all cancers in 4 years by 60%.⁴

When reviewing data on glucose metabolism disorders, the authors of the review found that prospective studies documented moderate to strong decreases while intervention studies with vitamin D supplementation had “little to no effect.”

However, in a recent study published in the Medical Journal of Australia, researchers found there is this inverse association between poor glycemic controlled gestational diabetes mellitus (GDM) with lower blood levels of 25[OH]D. 147 women with a mean gestational age of 35 ± 2 weeks were included, of whom 41% had insufficient or deficient levels of 25(OH)D (≤ 50 nmol/L). The study found lower 25(OH)D levels are independently associated with poorer glycaemic control.⁵

“It’s very consistent with other data on vitamin D and diabetes. Anything we can do to reduce risk for gestational diabetes is really important. That’s why I recommend all pregnant women should be on 2000-3000IU of vitamin D per day,” said Prof. Holick.

Prof. Holick added that vitamin D is not the cure-all for all serious chronic illnesses. Rather, practitioners should look to maintain adequate vitamin D status in their patients as a means to reducing risk.

“In a random controlled trial you should be looking at a baseline and a treatment level. If you’re going to give a standardised dose it should be based on that dose on all of the subjects in the trial. But the be all and end all should be ‘did these subjects raise their level of vitamin D?’,” said Prof. Holick.

According to the review, in 34 intervention studies that included patients with mean 25(OH)D concentrations less than 50 nmol/L at baseline, supplementation of 50mcg or 2000IU vitamin D did not show positive effect.

However, many of the cited studies did not measure blood level of vitamin D at the end of the study to know if there was a good compliance of taking the prescribed vitamin D.

In addition, Prof. Holick said, “Many of these reviewed studies were short-term and to expect short term vitamin D supplementation to reduce risk of cancers is a stretch at best.”

“It is most important for everybody to be aware that you should be maintaining a blood level of 25[OH]D throughout your life to reduce risk of these chronic illnesses.”

Prof. Holick said the results of some trials may also be a question of a suboptimal vitamin D dose.

“If you’re an overweight individual, you need more vitamin D to maintain that blood level of 25[OH]D. We like it to be above 75 nmol/L at a minimum and preferably at 100 nmol/L to 150 nmol/L is often what is suggested as the beneficial level to read 25[OH]D.”

Prof. Holick said while adults of a normal weight may be prescribed 1000-4000IU of vitamin D supplementation, overweight individuals may need vitamin D supplementation of up to 9000IU.

Research has found that obesity-associated vitamin D insufficiency is likely due to the decreased bioavailability of vitamin D3 from cutaneous and dietary sources because of its deposition in body fat compartments.⁶

In addition, Prof. Holick said subjects who are prescribed prednisone or anti-seizure medications need further adjustment to their vitamin D supplementation, as well as patients who have had gastric bypass surgery, and those with malabsorption syndrome or gastrointestinal issues.

References

Philippe Autier, Mathieu Boniol, Cécile Pizot, Patrick Mullie Vitamin D status and ill health: a systematic review. Lancet Diab Endo Dec 6 2013.
Low vitamin D in Victoria: Key health messages for doctors, nurses and allied health. Department of Health, Victoria, Australia, 2010.
Vieth R, Chan PC, MacFarlane GD. Am J Clin Nutr 2001;73(2):288-94.
Lappe JM, Travers-Gustafson D, et al. Vitamin D and calcium supplementation reduces cancer risk: results of a randomized trial. Am J Clin Nutr 2007; 85: 1586-91.
Lau SL, Gunton JE et al. Serum 25-hydroxyvitamin D and glycated haemoglobin levels in women with gestational diabetes mellitus. Med J Aust 2011.
Wortsman J, Matsuoka L Y, et al. Decreased bioavailability of vitamin D in obesity. American Society for Clinical Nutrition 2000.

Click here to read BioCeuticals' statement on vitamin D supplementation.