Lead is a heavy metal with deleterious effects on human physiology. In particular lead poisoning is known to cause neurological problems, and is particularly problematic in children because their nervous systems are still developing and are therefore more susceptible to metabolic poisons. Further, children are more efficient at absorbing nutrients which also places them at higher risk of lead poisoning. The symptoms of lead poisoning include pain, headaches, confusion, anaemia, seizures, convulsions, coma and eventually death. Lead can be absorbed through a number of routes, but nutritionists are most concerned with absorption through the gastrointestinal tract. A number of dietary factors have been identified that may increase lead absorption and these include iron deficiency, sodium citrate and some drugs. In contrast ethanol, high fat diets, as well as certain minerals including calcium, magnesium, phosphate and iron may limit lead absorption.
The effects of food in the gastrointestinal tract on lead absorption has been compared to the fasting state1. Subjects with low initial blood lead concentrations were fed a non-radioactive lead isotopes with either a single mixed meal or following 16 hours of fasting. Faecal excretion of lead was greatest during the first 5 days post dose, with little lead being excreted from day 11 onwards. However, not all of the lead tracer was recovered from the faeces and this can be accounted for by absorption. Calculation of the absorption based on the difference between faecal excretion and ingestion concentrations of lead showed that absorption of lead was 3 to 4 fold higher following a fast when compared to ingestion with food. Different chemical forms of lead did not affect the absorption rates. Analysis of the plasma showed that the lead isotope concentration in blood increased significantly following lead ingestion, and this rise in blood lead was correlated with the lead absorption rate calculated from faecal excretion.
The implication here then is that certain food components are able to inhibit the absorption of lead, although the mechanism may vary between food components. Mineral absorption is known to be competitive within certain classes of minerals, and the ability of certain divalent cations to inhibit the absorption of lead certainly suggests this might be so in the case of lead absorption rates. The evidence that iron deficiency increases lead absorption but supplemental and food iron decreases absorption suggests that lead shares a common route of absorption with iron. Of course this suggests that some of the deleterious effects of chronic lead intakes could be accounted for by decreased absorption rates of important trace minerals. Other components in food may contribute to the decrease in lead absorption. For example phytates in fibre are suspected of decreasing mineral absorption as they are able to bind to minerals and remove them from solution. Fibre may therefore bind lead in the gastrointestinal tract and inhibit its absorption.
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