Vitamin D And Your Health – Backgrounder

What is Vitamin D?

Vitamin D is a nutrient that helps the body use calcium and phosphorous to build and maintain strong bones and teeth. Too little vitamin D can cause calcium and phosphorus levels in the blood to decrease, leading to calcium being pulled out of the bones. This can cause rickets in children and osteomalacia (softening of the bones) or osteoporosis (fragile bones) in adults. However, too much vitamin D can cause too much calcium to be deposited in the body, which can lead to calcification of the kidney and other soft tissues including the heart, lungs and blood vessels.

What Are DRIs?

Dietary Reference Intakes (DRIs) are a comprehensive set of nutrient reference values for healthy populations established by Canadian and American scientists through a review process overseen by the Institute of Medicine (IOM) of the National Academies, which is an independent, nongovernmental body. Dietary Reference Intakes or DRIs are an umbrella term that describes four types of reference values: Estimated Average Requirement (EAR), Recommended Dietary Allowance (RDA), Adequate Intake (AI) and Tolerable Upper Intake Level (UL).

What Are the DRIs for Vitamin D?

DRIs for vitamin D were released in 1997 as part of the IOM’s review of Dietary Reference Intakes for all nutrients. For vitamin D, only an AI and UL were established.

The AI is based on the amount of vitamin D required to produce levels of serum 25-hydroxy vitamin D, an activated form of the vitamin in blood, considered to be adequate for those between the ages of six months and fifty. The Adequate Intake (AI) values for vitamin D, as currently expressed in the DRI tables, are as follows:

0-1 year: 200 IU per day
2 -50 years: 200 IU per day
51-70 years: 400 IU per day
> 70 years: 600 IU per day

The Tolerable Upper Levels of Intake (UL) for vitamin D for one year old and over is 2000 IU per day.

How Much Vitamin D Does Health Canada Recommend?

Until the DRIs for vitamin D have been updated, Health Canada continues to recommend that Canadians follow the advice contained in Eating Well with Canada’s Food Guide, which recommends that all Canadians over the age of two, including pregnant and lactating women, consume 500mL (two cups) of milk or fortified soy beverages every day for adequate vitamin D. Two cups of milk provide 200 IU of vitamin D, which is the Adequate Intake (AI) for everyone one year of age up to 50 years of age (as set out in the DRI tables).

What About Children?

While the AI value for children under one is listed in the DRI tables as 200 IU per day, Health Canada recommends that all breastfed, healthy term babies receive a daily vitamin D supplement of 400 IU and that children under the age of one receive 400 IU per day. This recommendation is to help reduce the risk of rickets, a disease that affects bone growth in children. Supplementation of the vitamin should begin at birth and continue until an infant’s diet includes at least 400 IU of the vitamin D from food sources or until the breastfed infant reaches one year of age. After one year, all children should have a daily intake of 200 IU of vitamin D, which is the amount found in two cups of milk or fortified soy beverage.

What About Adults Over the Age of Fifty?

The recommended vitamin D intake levels set for adults age 50 and over are based on the role of vitamin D and bone health. While Eating Well With Canada’s Food Guide provides sound nutrition advice for people over the age of 50, the amount of vitamin D in foods as recommended by the Food Guide is not enough to meet the Adequate Intakes necessary for people over the age of 50 to help reduce the risk of bone fractures. Therefore, for adults over the age of 50, Health Canada recommends that, in addition to following Canada’s Food Giude, everyone over the age of 50 should take a daily vitamin D supplement of 400 IU.

How Much is Too Much?

The Tolerable Upper Intake Level for anyone over one year of age is 2000 IU per day from all sources, including milk and supplements. Because of the potential adverse effects associated with taking too much vitamin D, it is recommended that this level not be exceeded.

Vitamin D Research

There has been a significant amount of information published on vitamin D requirements since the DRIs were published in 1997. In addition to the studies on the role of vitamin D in calcium metabolism and skeletal and muscular health, there have been studies on the association of vitamin D with cancers, autoimmune diseases and cardiovascular disease.

Some of this research has prompted various organizations in Canada to issue recommendations concerning increased vitamin D intake. Health Canada believes these recommendations are premature and that a comprehensive review that looks at both benefits and safety needs to be undertaken before we can issue revised recommendations for Canadians.

What is Health Canada Doing?

The Canadian Institute of Health Research (CIHR) is the Government of Canada's health
research funding agency. CIHR supports the work of more than 11,000 researchers across Canada and funds many research studies on vitamin D. The relevant research studies published in the scientific literature would form part of the evidence-base for the IOM’s review of the DRIs for vitamin D.

The U.S. Agency for Healthcare Research and Quality (AHRQ) was tasked to undertake a comprehensive and systematic review of the scientific literature on the relationships of vitamin D and calcium intakes to nutrient status indicators and health outcomes. This systematic evidence-based review, jointly funded by the American and Canadian governments, will be used to inform and support the DRI expert committee’s review of vitamin D and calcium reference values and will be released in 2009.

The Nutrition Research Division of Health Canada is currently conducting analyses on the vitamin D status of Canadians for the Canadian Health Measures Survey (CHMS). This national survey, being conducted in partnership with Statistics Canada, will provide the first national data on the vitamin D status of Canadians in over 35 years. This survey, which is collecting key health related information from over 5000 Canadians, will measure vitamin D levels as part of the assessment of chronic disease risk factors and nutritional status.

Health Canada scientists are also collaborating with researchers in Canadian universities studying vitamin D, specifically related to the status of young children who are not currently included in the CHMS.

The CHMS analysis on vitamin D will be finalized in 2010. Health Canada will be looking at the results of the CHMS survey and the results from the studies on vitamin D status of children in relation to the DRI recommendations for vitamin D and calcium that the IOM will issue following its review.

New Study to Review DRIs for Vitamin D and Calcium

The Institute of Medicine (IOM) has commenced a review – funded jointly by the U.S. and Canadian governments – of the Dietary Reference Intakes (DRIs) for vitamin D and calcium.

The Food and Nutrition Board of the IOM is putting together a committee of scientific experts for this review of vitamin D and calcium. As in previous DRI reviews conducted by the Food and Nutrition Board of the IOM, the expert panel reviewing the latest science related to vitamin D will be made up of experts from both Canada and the U.S.

This review will consider the evidence relating vitamin D to the reduction in the risk of cancers and other chronic diseases, as well as the evidence relating vitamin D to bone health. This review will also include an evaluation of safe upper intake levels and will look at considerations such as latitude, sun exposure and skin pigmentation.

The study is expected to take roughly two years, with the final report published in 2010