A study published in the British Medical Journal this month has reported that low vitamin D is associated with an increase in all-cause mortality and cancer mortality, but not cardiovascular mortality.
The three main sources of vitamin D are derived from sun exposure, supplements, and food such as cow’s milk, eggs, and vitamin fortified foods. Vitamin D has been linked with bone health and immune function. In some studies, low vitamin D has been associated with an increase in all-cause mortality, cardiovascular mortality, and cancer mortality, however clinical trials which have tested the benefits of vitamin D supplementation have failed to demonstrate clear and consistent benefits on all cause, cardiovascular or cancer mortality.
How much vitamin D do you need?
|Age group||Aim for an intake of international units (IU)/day||Stay below IU/day*|
|Infants 0-6 months old||400||1000|
|Infants 7-12 months old||400||1500|
|Children 1-3 years old||600||2500|
|Children 4-8 years old||600||3000|
|Children and Adults 9-70 years old||600||4000|
|Adults over 71 years old||800||4000|
|Pregnant and Breastfeeding Women||600||4000|
|*This includes vitamin D from both food and supplements|
(Source: EatRight Ontario Vitamin D Fact Sheet)
A recent study assessed the association between 25-hydroxyvitamin D concentrations and all-cause, cardiovascular, and cancer mortality. The study gathered participants from three cohorts: the Copenhagen City Heart Study, the Copenhagen General Population Study, and the Copenhagen Ischemic Heart Disease Study. In all, 95 766 participants of Danish descent were included in the study. The participants were assessed for genetic differences in DHCR7 and CYP2R1 genes that decrease levels of 25-hydroxyvitamin D in the plasma, which the researchers used to assess vitamin D status.
The results of the study revealed that low genetic levels of plasma 25-hydroxyvitamin D were associated with an increase in all cause, cancer, and other mortality, however there was no evidence of increase in cardiovascular mortality. While these associations were observed in the current study, intervention trials have failed to support a clear and consistent role for vitamin D supplementation in reducing mortality. A reason for this, as suggested by the authors, is that the genetic study is able to include all sources of vitamin D and its effects, via sun exposure, diet, and dietary supplements. In addition, the results would account for lifelong exposure to low levels of vitamin D. In contrast, intervention studies can only account for vitamin D levels via supplements, and over a relatively short time period. This may be the reason for the lack of positive results seen in intervention trials to date.
Despite the lack of effect seen, intervention trials remain the only way to assess the effects of vitamin D supplementation on health outcomes. Clinical trials for vitamin D supplements currently recruiting participants include studies designed to investigate the effects of vitamin D supplementation on:
- Fatigue (University of Zurich, Switzerland)
- Insulin Resistance & Cardiovascular Disease (Washington University School of Medicine, US)
- Urinary Incontinence (University of Alabama at Birmingham, US)
- Chronic Pain (Hospices Civils de Lyon, France)
- Osteoporosis (Winthrop University Hospital, US)
- Ulcerative Colitis (University of Chicago, US)
- Crohn’s Disease (University of Michigan, US)
Since millions of dollars are spent each year on vitamin supplements, these studies are crucial to determine whether taking supplements such as vitamin D have beneficial health outcomes.
Afzal, S, Brøndum-Jacobsen, P, Bojesen, SE, Nordestgaard, BG. “Genetically low vitamin D concentrations and increased mortality: mendelianrandomisation analysis in three large cohorts” BMJ 2014; 349 doi: http://dx.doi.org/10.1136/bmj.g6330 (Published 18 November 2014)
EatRight Ontario Vitamin D Fact Sheet. Available from: http://www.eatrightontario.ca/en/Articles/Nutrients-(vitamins-and-minerals)/What-you-need-to-know-about-Vitamin-D.aspx#.VHc-w5UtBjo Last Accessed Nov 27, 2014.
Clinicaltrials.gov “Effect of Vitamin D Treatment on Fatigue” Available from: http://www.clinicaltrials.gov/ct2/show/NCT02022475?term=vitamin+D&recr=Open&no_unk=Y&rank=15 Last Accessed Nov 27, 2014.
Clinicaltrials.gov “Vitamin D, Insulin Resistance, and Cardiovascular Disease” http://www.clinicaltrials.gov/ct2/show/NCT00736632?term=vitamin+D&recr=Open&no_unk=Y&rank=16 Last Accessed Nov 27, 2014.
Clinicaltrials.gov “Vitamin D Supplementation in Older Adults With Urinary Incontinence” Available from: http://www.clinicaltrials.gov/ct2/show/NCT01971801?term=vitamin+D&recr=Open&no_unk=Y&rank=20 Last Accessed Nov 27, 2014.
Clinicaltrials.gov “Chronic Pain and Vitamin D” Available from: (DOVID)http://www.clinicaltrials.gov/ct2/show/NCT02002000?term=vitamin+D&recr=Open&no_unk=Y&rank=22 Last Accessed Nov 27, 2014.
Clinicaltrials.gov “Vitamin D and Osteoporosis Prevention in Elderly African American Women (NIHD)” Available from: http://www.clinicaltrials.gov/ct2/show/NCT01153568?term=vitamin+D&recr=Open&no_unk=Y&rank=25 Last Accessed Nov 27, 2014.
Clinicaltrials.gov “Vitamin D Treatment in Ulcerative Colitis” Available from: http://www.clinicaltrials.gov/ct2/show/NCT01640496?term=vitamin+D&recr=Open&no_unk=Y&rank=51 Last Accessed Nov 27, 2014.
Clinicaltrials.gov “Trial of High Dose Vitamin D in Patient’s With Crohn’s Disease (RODIN-CD)” Available from: http://www.clinicaltrials.gov/ct2/show/NCT02208310?term=vitamin+D&recr=Open&no_unk=Y&rank=55 Last Accessed Nov 27, 2014.
Image courtesy of foto76 at FreeDigitalPhotos.net
Written by Deborah Tallarigo, PhD