Anaemia and iron deficiency in children and women in Tanzania. Effects of dietary iron intake, low iron bioavailability and supplementation with multiple micronutrient beverage

Sammanfattning: Anaemia was investigated in a rural Tanzanian community to determine its magnitude and causative factors in different population groups. Nutritional anaemia resulting mainly from a diet with a low bioavailability of iron affected more than half of the total number of women and children. As in many developing countries, a high consumption of cereals and a vegetable-based diet known to contain phytate, an inhibitor of iron absorption, was common. Household dietary surveys showed that maize, sorghum, millets, peas, beans, nuts and green leafy vegetables made up 80% of the major sources of dietary iron.

This thesis reports on studies of the long-term effects of iron intake from foods in the study area, effects of low dietary iron bioavailability and effects of interventions using a multiple micronutrient beverage on anaemia status in children and pregnant women.

In the nutritional survey conducted in a multistage cluster sampling design, 80% of preschool children (aged < 5 y), 67% of the schoolchildren (aged 5-14 y) and 74% of the pregnant women (17-45 y) were found to be anaemic. Multiple aetiological factors (nutritional and health related factors) were found to be associated with the anaemia; however, iron deficiency (erythrocyte protoporphyrin > 125 µmol/mol haem or serum ferritin < 20 µg/L) was found to correlate significantly with the anaemia, p<0.05, and was a high risk factor for anaemia (RR ~2.0). Of the preventable factors for anaemia in the study population, iron deficiency had the highest attributable fraction of 33%.

Mean dietary iron intake was found to be significantly (p < 0.05) lower in the anaemic than the non-anaemic schoolchildren (22 vs 27 mg/d, respectively). Iron intake was found to be below the recommended daily allowance (FAO/WHO) for a very low iron bioavailability diet. Daily meat and fruit intake was low. Iron bioavailability (estimated in vitro) from composite meals was very low (< 5%) giving an iron intake below the recommended daily intake in 50% of the investigated children. In addition to iron deficiency the risk of anaemia was also high in subjects with vitamin A deficiency, malaria and helminthic infections. In multiple linear regressions analysis iron deficiency was the significant predictor of anaemia status in all population groups. In adolescents and adults a low body mass index, hookworm and schistosomiasis were additional significant factors (p < 0.05).

A randomised, placebo-controlled efficacy trial with a beverage containing iron, iodine, vitamin A, vitamin C, zinc, riboflavin, niacin, folate, vitamin B12, vitamin B6 and vitamin E at physiological doses increased the haemoglobin concentration by 9.2 g/L in anaemic children and by 8.6 g/L in pregnant women after a supplementation period of six and two months respectively. The risk for anaemia in the study subjects taking the fortified beverage was reduced by 20% in children and 50% in pregnant women (RR=0.79 and 0.49 respectively). Predictors for haemoglobin increase at the end of follow-up period were supplementation with micronutrient beverage, and haemoglobin, ferritin and retinol status at the beginning of the study, and, in pregnant women, gestational age at entry into the study.

It is concluded from these studies that the high anaemia rates early in childhood and in pregnancy are related to the diet consumed by the study population and that food-based strategies that promote increased intake of micronutrients are a suitable option for its prevention. An efficacy study with a multiple micronutrient beverage provided on a daily basis to children and pregnant women proved that the beverage was effective in reducing iron deficiency anaemia.

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