Vitamin D and Calcium: Updated Dietary Reference Intakes

The U.S. Institute of Medicine (IOM) released its report on the review of the  Dietary Reference Intakes (DRIs) for vitamin D and calcium on November 30, 2010.  The review was jointly commissioned and funded by the U.S. and Canadian governments.

The decision to commission the IOM review reflects the government's goal of ensuring that Canadians benefit from the most up to date health and nutritional advice.

The IOM report states that there is no additional health benefit associated with vitamin D or calcium intakes above the level of the new Recommended Dietary Allowance (RDA). Health Canada reminds Canadians that total nutrient intake should remain below the level of the new Tolerable Upper Intake Level (UL) to avoid possible adverse effects.

Questions and Answers on the DRI Process

• What are DRIs?
• Why review the DRIs for vitamin D and calcium?
• What process did the IOM use to conduct its review?
• What were the conclusions about the relationship of calcium and vitamin D to chronic disease?
• What research gaps were identified?

Questions and Answers on updated DRIs for calcium and vitamin D

• What is Calcium?
• What are the new DRIs for Calcium?
• What foods provide calcium?
• What is the calcium status of Canadians?
• What is Vitamin D?
• What are the new DRIs for Vitamin D?
• What foods provide Vitamin D?
• What about sun exposure?
• Are there special considerations for vitamin D intake of certain sub-populations, such as those with darker skin or those who live at high northern latitudes?
• Did the IOM report make recommendations with respect to serum vitamin D levels?
• What is the vitamin D status of Canadians?

What are DRIs?

Dietary Reference Intakes (DRIs) are recommendations for nutrient intakes. They 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 in the United States.

Values for vitamin D, calcium, and other nutrients are set through the DRI process.

Why review the DRIs for vitamin D and calcium?

The DRIs for vitamin D and calcium were first published in 1997.  Since that time, a significant amount of information has been published on vitamin D requirements and on the association of vitamin D with chronic diseases and conditions.  Because of the availability of sufficient new and relevant scientific research to warrant a re-evaluation of the existing values, Health Canada, the Public Health Agency of Canada, and several U.S. government agencies co-sponsored a review of the DRIs for vitamin D and calcium.

The decision to commission the Institute of Medicine (IOM) review reflects the government's goal of ensuring that Canadians benefit from the most up-to-date health and nutritional advice.

What process did the IOM use to conduct its review?

The Food and Nutrition Board of the Institute of Medicine (IOM) put together a  committee of scientific experts for this review of vitamin D and calcium in January 2009. 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 and calcium was made up of experts from both Canada and the U.S.

The IOM's process for the review of data on vitamin D and calcium was rigorous. The 14-member expert committee gathered background information on the metabolism of vitamin D and calcium throughout the life cycle. Then, using a risk assessment approach, they identified potential health-outcome indicators for establishing DRIs. Important documents for this phase were the two evidence-based systematic reviews conducted by the U.S. Agency for Healthcare Research and Quality on the  effectiveness and safety of vitamin D in relation to bone health and the  relationships of vitamin D and calcium intakes to nutrient status indicators and health outcomes, conducted at the request of the U.S. and Canadian governments. The committee also performed their own systematic review of scientific literature and identified other relevant studies.

Canadian data from the Canadian Community Health Survey Cycle 2.2, Nutrition, and the Canadian Health Measures Survey were used in the IOM review.

The committee developed recommendations for adequacy (Estimated Average Requirements and Recommended Dietary Allowances) and for preventing excessive intakes (Tolerable Upper Intake Levels) based on this extensive data review. Finally, the committee outlined the implications of its work and identified research needs to aid development of DRIs for vitamin D and calcium in the future.

What were the conclusions about the relationship of calcium and vitamin D to chronic disease? 

The IOM expert committee reviewed a number of health outcomes that could potentially be related to calcium and vitamin D, such as cancer, cardiovascular disease, diabetes, and immunity, and found that the evidence existing to date is inconsistent and does not demonstrate a cause-and-effect relationship. Consequently, these health outcomes could not be used for the purposes of determining nutrient requirements.

The evidence surrounding the role of calcium and vitamin D in bone health was judged to be convincing, and was used as the basis for determining requirements for calcium and vitamin D.

What research gaps were identified?

The IOM expert committee identified areas where further research would help improve the determination of reference values in the future.  A total of 22 major research needs were identified and are summarized in  Table 9-1 of the report. The general categories of information gaps are:

• Data on the physiology and metabolism of calcium and vitamin D
• Data on health outcomes and adverse effects related to calcium and vitamin D
• Data on dose-response relationships between intakes of calcium and vitamin D and health outcomes
• Evidence to judge independent effects of calcium and vitamin D
• Information on the impact and role of sun exposure relative to vitamin D
• Standardized and consistent data on calcium and vitamin D intakes
• Exploration of methodologies for synthesizing evidence

What is Calcium?

Calcium is the most abundant mineral in the body. Over 99% of the body's calcium supply is found in the bones and teeth where it supports their structure. Calcium is also important for proper muscle function, nerve transmission, and hormonal secretion.

What are the new DRIs for Calcium?

The DRIs for calcium are based on evidence related to bone health, largely from the results of calcium balance studies. Calcium balance, which can be positive, neutral or negative, compares total calcium intake with urinary and fecal excretion of calcium. It is used to determine the accumulation and level of bone mass.

The DRIs for calcium^{Footnote 1}, which can also be found in the DRI tables, are as follows:

The IOM report states that there are no additional health benefits associated with calcium intakes above the level of the new RDA.

Total calcium intake should remain below the level of the new UL to avoid possible adverse effects. Long-term intakes above the UL increase the risk of adverse health effects, such as kidney stones.

What foods provide calcium?

Calcium is found in many foods. You can get recommended amounts of calcium by eating a variety of foods, including the following:

• Milk and milk alternatives such as yogurt, cheese, and fortified plant-based beverages (such as fortified soy beverage)
• Dark green vegetables such as broccoli, kale and spinach
• Fish with soft bones that are eaten, such as canned salmon or sardines.

What is the calcium status of Canadians?

Information on calcium intakes is available from dietary intake data, collected in the 2004 Canadian Community Health Survey (CCHS). At a national level, the prevalence of inadequate calcium intake varies widely, but tends to increase with age and is higher in women than men.

Based on food intakes only:

• Only about 3% of children aged 1-3 had inadequate intakes of calcium.
• Almost one-quarter (23%) of children aged 4-8 had inadequate intakes of calcium.
• More than one third (33-44%) of boys aged 9-18 and more than two-thirds (67-70%) of girls aged 9-18 had inadequate intakes of calcium.
• Adult men had a prevalence of inadequate intakes ranging from 27-80%, depending on the age group.
• Adult women had a prevalence of inadequate intakes ranging from 48-87%, depending on the age group

Data on calcium intakes from food and supplement sources combined show that supplement use did not greatly affect the prevalence of inadequate calcium intakes in most age and gender groups, with the exception of women over the age of 50.

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. Vitamin D is unique in that it can be synthesized by the body after exposure to ultraviolet rays from sunlight.  Too little vitamin D can cause calcium and phosphorus levels in the blood to decrease, leading to calcium being pulled out of the bones to help maintain stable blood levels. 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 the new DRIs for Vitamin D?

The DRIs for vitamin D are based on maintaining skeletal health and have been set using the assumption that sun exposure is minimal.

The DRIs for vitamin D, which can also be found in the DRI tables, are as follows:

The IOM report states that there are no additional health benefits associated with vitamin D intakes above the level of the new RDA.

Total vitamin D intake should remain below the level of the new UL to avoid possible adverse effects. Long-term intakes above the UL increase the risk of adverse health effects.

What foods provide Vitamin D?

The major sources of vitamin D are fortified foods. In Canada, cow's milk and margarine must be fortified with vitamin D. Goat's milk, fortified plant based beverages (e.g., fortified soy beverages), and some calcium-fortified orange juices are permitted to be fortified with vitamin D. Cheese and yogurt can be made with vitamin D-fortified milk, however, the final product does not contain as much vitamin D as fluid milk alone. The only natural sources of vitamin D in the Canadian food supply are fatty fish and egg yolks.

Because it is a commonly-consumed food, fluid milk is a major dietary source of vitamin D.

What about sun exposure?

The DRIs for vitamin D are set based on the assumption of minimal sun exposure. This was necessary because of public health concerns about skin cancer due to ultraviolet radiation from the sun.  Currently, there is a lack of information about whether sun exposure may be experienced without increasing risk of cancer.

Many people meet at least some of their vitamin D needs through exposure to sunlight.  However, season, time of day, cloud cover, smog, skin pigmentation, and sunscreen use are all factors that can affect the amount of ultraviolet radiation received and thus vitamin D synthesis.

The DRI values have been set at levels that ensure that sun exposure is not necessary in order to obtain enough vitamin D.

Are there special considerations for vitamin D intake of certain sub-populations, such as those with darker skin or those who live at high northern latitudes?

The DRIs for vitamin D have been set assuming minimal sun exposure for all, which means that additional recommendations are not required for sub-populations such as those at high northern latitudes, those with darker skin pigmentation, or those with heavy clothing that inhibits sun exposure.

Did the IOM report make recommendations with respect to serum vitamin D levels?

Serum concentration of 25-hydroxy-vitamin-D (25(OH)D) is the best indicator of vitamin D status.  It reflects total vitamin D input - from food, supplements, and sun exposure.

There is considerable discussion surrounding the serum concentrations of 25(OH)D associated with optimal health, and cut points have not been developed by a scientific consensus process.

However, the IOM expert committee stated that its review of the data suggests that, relative to bone health:

• People are at risk of vitamin D deficiency (rickets or osteomalacia) at serum 25(OH)D concentrations <30 nmol/L. Some are potentially at risk for inadequacy at levels ranging from 30–50 nmol/L.
• Practically all people are sufficient at levels ≥50 nmol/L
• There may be reason for concern at serum concentrations >125 nmol/L

The IOM expert committee encouraged the development of evidence-based cut points for serum vitamin D measures relative to deficiency as well as excess.

What is the vitamin D status of Canadians?

Vitamin D status can be measured in two ways - vitamin D dietary intakes, and vitamin D blood levels. It is the blood level data that gives a true picture of the vitamin D status in the body. Vitamin D is unique in that there is another source besides diet and supplements, namely, sunlight. So even if dietary intakes do not appear to be adequate, overall vitamin D status may be much different.

Dietary intake data were collected in the 2004 Canadian Community Health Survey (CCHS). At a national level, there seems to be a very high prevalence of inadequate vitamin D intakes from food sources (range 75-96%; with most age and gender groups having about 90% prevalence of inadequate intakes.)

Data on vitamin D intakes from food and supplement sources combined show a lower prevalence of inadequate vitamin D intakes, although still above 50% (range 54-84%, depending on age and gender).

However, estimates of inadequate intakes of vitamin D must be interpreted with caution because the reference values to assess adequacy assume no vitamin D is contributed to the body by sun exposure. For this reason, data on vitamin D intakes from food and supplement sources cannot stand alone and consideration must be given to serum 25-hydroxy-vitamin-D (25(OH)D) levels, a well-established biomarker for vitamin D status.

The Canadian Health Measure Survey (CHMS) was conducted from 2007 to 2009 and collected blood samples, from which vitamin D status can be assessed.  While there appears to be a high prevalence of inadequate intakes of vitamin D from dietary sources, available clinical measures do not suggest wide-spread vitamin D deficiency in the Canadian population^{Footnote 2},^{Footnote 3}. Vitamin D status in some sub-populations, however, may warrant further consideration.