Title: The Desirability Of Extending The Current Level Of Iron Fortification Of Foods In The Uk

 

Key words: iron, deficiency, anaemia, anemia, iron stores, iron intake, dietary iron, supplements, supplementation, iron absorption, vitamin C, red meat, bioavailability, phytates, polyphenols, genetics, fortification, CHD, coronary heart disease, acute myocardial infarction, ferritin, atherosclerosis, haemochromatosis, colonic cancer, iron overload, cancer, infection, SIDS, pre-eclampsia, transferring, lipid peroxidation, homeostasis, cognitive problems, depletion, vegetarians, South Asian, minority groups,

Date: Sept 2006 

Category:

Nutrimed Module:

Type: Article 

Author: Morgan, G

 

 

The Desirability Of Extending The Current Level Of Iron Fortification Of Foods In The UK

 

Iron deficiency remains worldwide the most common of all the micronutrient deficiencies with an estimated 30% of the world’s population suffering from anaemia (WHO 1997). In industrial countries the incidence has been estimated as much lower at between 2-8%. However, the incidence of iron store depletion is much higher than this, with incidences rising to 33%, for example, amongst women of childbearing age in the UK (Gregory 1990). This group, children and adolescents remain the most vulnerable and are the groups of most concern to the providers of health care in the developed world.

 

There has been a gradual decline in iron intakes in the UK over the last 30 years (Millward 2002), in spite of government food supplementation measures. Supplementation accounts now for 20% of the dietary intake yet total intakes have continued to decline. Surveys have identified the major contributors to this decline over the last 50 years (MAFF 1991b). During this period bread consumption has shown a steep decline with a lesser fall in vegetable consumption. Meat intake, the other major source of iron and an important promoter of iron absorption, has remained largely unchanged. A rise in fruit, and especially fruit juice, consumption has failed to compensate for a decline in vitamin C intake, the other major promoter of iron absorption.

 

Cultural diversity in the UK poses major problems for any national health policy aimed at improving the iron status of the nation. Iron absorption from food-to-food varies enormously, from less than 1% to greater than 50% (Yip 2001) depending on bioavailability factors. Meat and vitamin C help to promote absorption, whereas foods high in phytates and polyphenols such as bread and other cereals, and tea consumption, impede iron absorption. Sizeable minority groups such as vegetarians and South Asian communities therefore find themselves at a significant disadvantage. Genetic factors may also play a part. The US black community, for example, has been shown to be genetically more prone to anaemia than comparable white groups (Johnson-Spear 1994). Any fortification policy should take account of such factors.

 

Objections To Iron Fortification

Objections have been raised against plans to further raise the level of iron supplementation in the UK diet. These objections relate to issues of enormous public health concern and call for serious review. The following issues have received most attention:

1)     Coronary heart disease. A Finnish study (Salonen 1992) showed a two-fold increase in the rate of acute myocardial infarctions in men with raised ferritin levels. A subsequent large study was unable to replicate these results (Sempos 2000) and it is now thought that raised ferritin levels reflect an acute phase protein reaction associated with the inflammatory vascular endothelial reaction of atherosclerosis (Alexander 1994). Significantly it has been found that haemochromatosis patients with iron overload do not have an increased incidence of coronary heart disease (Powell 1994).

2)     Colonic cancer. One study demonstrated an increased incidence of cancer of the oesophagus, bladder and colon in association with elevated iron stores (Stevens 1988). A subsequent large prospective survey has failed to show an association (Selby 1988). There have been several studies, however, that have shown an association between high iron intake and colonic cancer (Knekt 1988, Nelson 1989). A local oxidative effect of iron radicals on the colonic mucosa leading to cancerous changes has been postulated. In view of the higher incidence of colonic cancer in red meat eaters (World Cancer Research Fund 1997, Bingham 1996), this possibility needs to be taken seriously and warrants further research to determine the precise mechanisms involved.

3)     Haemochromatosis. This autosomal recessive condition is associated with increased iron absorption, iron overload and the development of iron deposition in the liver, endocrine glands and heart. Cirrhosis and heart failure may be insidious and hard to detect until too late. The homozygote state affects about 1 in 400 of the population and the milder heterozygote state about 1 in 10. Ferritin levels in around 20% of heterozygotes are raised but, in spite of increased uptake and stores in both the homo- and heterozygote forms, there is no evidence that patients on normal or supplemented diets have an incremental rate of increased iron absorption and deposition (Cartwright 1979), nor that if this were the case that the additional homozygous iron overload levels of 20-40 grams would ever be reached by heterozygotes following many years of iron supplementation.

4)     Immunity. Both anaemia and iron overload have been associated with increased incidences of infectious diseases, particularly in tropical countries where iron supplementation has been linked with, for example, increased rates of malaria (see Walter 1997 for review). There is no convincing evidence that iron supplementation in the developed world is at all harmful to the immune system.

5)     SIDS (Sudden Infant Death Syndrome). Post-mortem studies of SIDS cases have shown findings consistent with iron overload. It is likely that these represent post-mortem findings as a prospective study has shown no such associations ( Worwood 1995).

6)     Pre-eclampsia toxaemia. Although iron overload with increased saturated transferrin and ferritin levels is characteristic of pre-eclampsia, this condition is not associated either with increased preconceptual iron stores or increased iron intake during pregnancy (Eastman 1983, Hubel 1996). Immune dysregulation leading to placental intravascular haemolysis or extravascular destruction of red blood corpuscles with the release of free iron radicals and a cascading lipid peroxidation reaction appears to be the pathological mechanism involved. Low levels of transferrin and possibly other antioxidants predispose to the condition (Hubel 1996).

 

The Continuing Case For Iron Fortification

Consideration of the above arguments leads one to conclude that, apart from the possible exceptions of colonic cancer and the the homozygous haemochromatosis state, there is little evidence to warrant not implementing a policy to further fortify the UK diet. Iron homeostasis is very sensitive and iron absorption has been shown to shut down when intake exceeds demands (Hallberg 2000). As pointed out earlier, increased iron intake has not, to date, been shown to speed up the onset of haemochromatosis and it would be more appropriate in this context to institute a screening programme to help identify such a relatively common and treatable condition. Colonic cancer is now one of the more prevalent cancers and public health measures need to address any possible dietary associations of this disease. Increased awareness, screening and the present government policy of implementing its ‘At Least Five a Day’ plan to increase fruit and vegetable consumption would appear to be the way forward.

 

Against this background there continues to be concern over the long-term effects of sub-optimal iron nutrition in the community. This is particularly the case with respect to child nutrition due to the relatively high incidence of iron deficiency in the UK in this age group. Cognitive, developmental and behavioural problems have been linked to chronic iron deficiency and the possibility raised that these may be non-reversible (Lozoff 1988, Lozoff 2000). This is of especial cause for concern. Amongst the adult population pregnant women with depleted iron reserves remain a major problem.

 

Though there is no firm evidence that borderline anaemia has any deleterious effects on gestation and routine monitoring is able to manage any iron related problems, depleted iron reserves following pregnancy are difficult to correct and leave long-term repercussions in terms of malaise, ill health and loss of work.

In the light of the continuing relatively high rates of iron deficiency amongst these groups and amongst vegetarians and the continuing decline in dietary iron consumption, it seems appropriate to recommend further fortification of iron to food. Bread and cereals remain a staple food and fortification of these foodstuffs would be most likely to target the most vulnerable groups in the population. Such programmes are feasible and effective as has been seen in countries such as the US, Sweden and Venezuela (Yip 1987, Hallberg 1979, Layrisse 1996).

 

References

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