Vitamin D: Why 25 is an important number

July 27, 2015

Hot on the heels of the Carbohydrates and Health report this week, the Scientific Advisory Committee on Nutrition (SACN) – the independent body of experts that advise government on nutrition recommendations – published its draft recommendations on vitamin D.

Major recommendations to emerge from the draft report include:

  • An intake of 10 μg (micrograms) vitamin D is recommended for all of the population over 1 year old
  • Serum 25(OH)D concentrations (level of vitamin D in the blood) should not fall below 25 nmol/L in order to protect musculoskeletal (bone and muscle) health

Where do we get vitamin D from?

There are two sources of vitamin D: Diet and exposure to sunlight (skin synthesis). The main dietary sources of vitamin D are foods of animal origin (oily fish, egg yolks and some meats), fortified foods (like breakfast cereals and fat spreads) and supplements. However, skin synthesis is the main source of vitamin D for most people, but typically is only effective between March and September.

It was assumed previously that, for most people, the amount of vitamin D produced by exposure to sunlight in summer months would be adequate for achieving serum 25(OH)D concentrations above 25 nmol/L during winter. This report indicates this is not the case. To avoid low vitamin D status, SACN is therefore proposing a dietary intake of 10 µg vitamin D per day.

SACN was not able to recommend how much sunlight exposure people would need in order to achieve vitamin D blood levels of 25 nmol/L because there are many factors that affect vitamin D production in the skin.

Are the draft SACN recommendations new?

Current UK government advice is that only certain groups of the population, who are at risk of vitamin D deficiency, are advised to take a daily supplement. This includes pregnant and breastfeeding women, infants and children aged under 4 years, people over 65 years and those with limited exposure to the sun (e.g. if they cover their skin for cultural reasons or are housebound). One of the major changes to emerge from the draft report is that there was previously no recommendation on vitamin D intake for the general population, but now there is.

What in the report may be of particular interest to the care home population?

Falls are a common and a serious problem for older people in residential or nursing care facilities, and may cause loss of independence, injury and sometimes death as a result of injury.  The draft SACN report provides a useful summary of research on vitamin D in respect to falls. The Committee conclude that whilst the evidence on vitamin D and falls is mixed, overall it is suggestive of a beneficial effect of vitamin D supplementation in reducing fall risk in adults > 50 years.

How much vitamin D are older people getting in their diet?

Current dietary survey data only includes free-living older people. The last national dietary survey measurements recorded on institutionalised older adults were some 20 years ago. This reported mean daily vitamin D intake from all sources (including supplements) to be 3.87µg for men and 3.36µg for women, and found around 38% of men and women had low vitamin D status with plasma concentration less than 25 nmol/L.

Current dietary data reports that around 20% free-living older people aged 65+ have mean plasma concentrations below 25 nmol/L, but it is likely that there would be a higher prevalence of low vitamin D status in residents of care homes.

The draft recommendations are now out for public consultation. In the meantime, for the over 65 age group, there are already recommendations to increase the use of vitamin D supplements to prevent deficiency among those most at risk, and to increase consumption of dietary sources of vitamin D such as oily fish, meat and eggs.

Ayela Spiro, British Nutrition Foundation – QCS Expert Nutrition Contributor


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