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Vitamin D Status

Vitamin D status is measured using serum 25(OH)D levels. This reflects vitamin D derived from food or endogenous synthesis.¹ Vitamin D deficiency is defined as a serum 25(OH) level < 37.5 nmol/l in adults or < 27.5 nmol/l in infants and children.¹ The suggested target for optimal level of 25(OH)D in adults is widely accepted as ≥ 75 nmol/l.¹ However, according to the new Dietary Reference Intakes (DRI) published by the Institute of Medicine, a level of 25(OH)D above 20 ng/mL (or 50 nmol/L) is sufficient for good bone health for practically all individuals.² Vitamin D can be obtained via endogenous synthesis upon skin exposure to UVB (290-310 nm) or through foods.¹

Factors influencing endogenous synthesis of vitamin D include:¹

• Latitude,
• Limited time spent outdoors,
• Skin pigmentation,
• Age,
• Sunscreen/clothing.

In countries above 40˚ north latitude (including Canada) or below 40˚ south latitude, UVB radiation is not strong enough for endogenous synthesis to occur during the winter months.¹

Individuals who are not able to be outdoors are vulnerable year-round.¹

The skin pigment melanin can reduce photosynthesis of vitamin D by 50-fold, therefore individuals with darker skin are at higher risk for vitamin D deficiency.¹

Endogenous synthesis of vitamin D decreases with age.¹

Sunscreen with a sun protection factor (SPF) of 8 or more also suppresses endogenous synthesis of vitamin D.¹

Improving vitamin D status

Since ongoing endogenous synthesis is problematic, maintaining adequate vitamin D status depends on body stores of vitamin D and intake from dietary sources.³

With respect to dietary sources, only a few foods contain vitamin D naturally (e.g. fatty fish, egg yolks, and fish liver oils) and these foods are not consumed on a regular basis.³

A systematic review published in 2008 evaluated the efficacy of vitamin D-fortified foods on serum 25(OH) concentrations.³

• Fortified foods contribute ~ 65-86% of the total daily vitamin D intake from foods with milk contributing ~ 40-64%;
• Nine randomized controlled trials (n = 889 US adults) were included in the systematic review;
• Eight of the nine studies consistently showed a significant beneficial effect of food fortification on 25(OH) concentrations;
• The authors concluded that vitamin D-fortified foods improved vitamin D status in US adults.

In March 2010, Statistics Canada released the findings from their Canada-wide survey, the Canadian Health Measures Survey (CHMS), examining the vitamin D status of Canadians. This survey polled 5,306 Canadians aged 6 to 79 years. Please see the article “Vitamin D Status of Canadians” for more details.⁴

Factors associated with suboptimal vitamin D status included:⁴

• Winter season,
• Racial background other than white,
• Less frequent consumption of milk.

The frequency of milk consumption tended to be positively related to 25(OH)D levels.⁴

People who consumed milk more than once a day had a mean concentration of 75 nmol/l vs. 62.7 nmol/l among those who did so less than once a day.⁴

Keywords: vitamin d, survey on vitamin d, data on consumption, statistics canada

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