N08017: How can we identify schoolgirls at risk of low iron status and what dietary advice should we be giving?

Study Duration: July 2001 to September 2002

Contractor: SiG – Nurture Nutrition Consultancy

A significant proportion of schoolgirls in Britain may be deficient in iron. This is due to a combination of increased growth and their periods starting and can be made worse by the low intake of iron from their diets.

The recent Government-funded National Diet and Nutrition Survey (NDNS) of Young People aged 4 to 18 years (published in 2000) showed that over a quarter (27%) of the oldest girls aged 15 to 18 years had low iron stores while 9% were classified as anaemic. This project was commissioned to carry out a further analysis of this NDNS data to identify the main dietary and physiological factors associated with low iron status, and adequate iron status, in girls aged 7 to 18 years.

Those who took part in the National Diet and Nutrition Survey of Young People aged 4 to 18 years (published in 2000) were asked to weigh and record all food and drink consumed over seven days. Many also provided a blood sample which was analysed for indicators of iron status.

The characteristics of those girls aged 7 to 18 years who were classified as having 'low' iron status were compared to the characteristics of those who had 'adequate' iron status. Statistical modelling was then used to identify the main predictors of low iron status and good iron status.

The results were used to derive a scoring tool designed to evaluate the risk of iron status in this population group, and devise associated dietary messages targeted at young girls to help improve their iron status.

There has been some delay in publication of the results for this project due to additional statistical analyses undertaken, and the subsequent evaluation and consultation process.

30% of the girls had at least one of the indicators of low iron status as defined for this project, i.e. low haemoglobin, ferritin or transferrin saturation levels.

Characteristics that predict low iron status
The best model predicting low iron status was based on one physiological characteristic (menarche) and three dietary characteristics (red meat, fruit or fruit juice, and tea). Girls who had started having periods were more likely to have low iron status. Eating no red meat at all during the survey week was associated with more than treble the odds of low iron status, compared with eating red meat most days (more than 90 grams/day). Consuming neither fruit nor fruit juice during the 7 day dietary recording period doubled the odds of having low iron status. Drinking more than one cup of tea (125ml) per day was associated with almost double the odds of low iron status, while lesser amounts were not associated with significant excess risk. Eating raw vegetables (salads) at least once during the seven-day dietary recording period doubled the odds of good iron status and this, too, was included in the scoring tool.

Scoring tool
A scoring tool was produced from the best models and this correctly classified about 65% of the overall sample. This level of accuracy is regarded as fair rather than good, but better than a prediction based on total iron intake. The Agency has decided that the scoring tool requires further testing and validation prior to any future potential use.

Dietary messages
The following messages are based on the results of this project, together with other scientific evidence of dietary habits relevant to iron status.

• Red meat (beef, lamb, pork, offal) is rich in iron that is easily absorbed (haem iron), the darker the meat the more iron it contains
• Poultry contains some haem iron, and leg meat contains more iron than breast meat
• Fish contains some haem iron too, especially oily fish and molluscs (mussels, etc)

If you are vegetarian so eating no meat or fish, the following messages are even more important for you:

• Fresh fruit or fruit juice with meals greatly helps to improve iron absorption
• Salad vegetables (including tomatoes) contain vitamin C to help iron absorption
• Green leafy vegetables contain some iron (e.g. watercress, kale)
• Avoid drinking tea with meals (or within 30 minutes of a meal) as this greatly reduces iron absorption
• If you have heavy periods you may need extra iron
• See your doctor if you think you may be anaemic

Benefits of the research and further opportunities
The messages resulting from this project emphasise not just the amount of iron, but the importance of the type of iron (haem or non-haem) and the effect of other dietary constituents that can reduce or increase iron absorption. The Agency will be considering how best to disseminate these messages, which provide an evidence-based approach to dietary advice targeted at this population group. In addition, if validated, the scoring tool may provide a non-invasive, rough guide to likely risk of low iron status for young girls, which could be linked to the above dietary messages.

Final report is available from the FSA Library and Information centre.
To obtain a copy, please contact the Enquiry Desk, Dr. Elsie Widdowson Library and Information Services, Food Standards Agency (020 7276 8181/8182 or at library&info@foodstandards.gsi.gov.uk).

Contact: For any enquiries concerning this research project, please contact the relevant Programme contact or email science@foodstandards.gsi.gov.uk