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Harmful traces

TRACE ELEMENTS IN HUMAN NUTRITION AND HEALTH·World Health Organization, Geneva, Switzerland· Pages 343

By Mohammed Zeyaul Haque
Published: Thursday 15 January 1998

Nutritional deficiencies can i (Credit: CSE)trace elements, that form a part of human nutrition, are not well understood. These substances, occurring in small amounts (especially in the soil) are usually needed in extremely small measures for the proper growth of plant and animal life. However, they can become toxic even in relatively low dosages. Also, a few of them are totally toxic and do not have any known nutrition value.

The World Health Organisation (who) has always been interested in standardising nutrition and health parameters for population groups, keeping in view their geographical situation, eating habits, cultural preferences related to food, and the availability of food in their locality.

who , which has access to health professionals of 190 member-countries exchanging data on health and nutrition, had formed an expert committee on trace elements in 1973 to examine "trace elements in human nutrition" to address issues concerning the essentiality of, requirements for, and metabolism of 17 trace elements in humans. The committee came up with recommended intakes for populations widely differing in the content and bioavailability of trace element constituents.

However, over the years the sophistication in the technology of analysis has increased manifold. Even some new trace elements have been discovered. The knowledge of nutrition has grown tremendously. Hence, who arranged a number of workshops and consultations in collaboration with the food and agriculture organisation of the United Nations (un) and the International Atomic Energy Agency.

This book is a compilation of the studies involving 19 nutritionally significant trace elements ranging from essential elements like iodine and zinc, elements like manganese and silicon that are suspected to be essential, and others like arsenic and lead that can be toxic but may have some essential functions.

The study is significant because an attempt has been made to establish more sophisticated methods of evaluation of trace element intake and its safe ranges for population groups in terms of both deficiency and excess and imbalances. This would go a long way in improving nutrition planning and assessments of observed intakes, as a step towards the diagnosis and control of disorders related to trace elements.

That this is relevant for India in terms of tackling deficiency and excess is quite obvious. To illustrate the point, we have widespread iodine deficiency in the Himalayan region because of leaching, and in the Gangetic plains where floods wash away much of the iodine in the soil. Also, we have an extremely high incidence of a certain kind of paralysis in parts of Unnao district because of the high concentration of manganese in local water. The problem of skeletal flourisis among the population in parts of Rajasthan is because of excess of fluorine in water there.

The study is important because of many considerations. It takes into reckoning the interaction between different elements. It is interesting to note that the bioavailability of certain elements is inhibited by some elements while it is enhanced by certain others. These factors are extremely important in determining safe ranges of intake. Also, the physiological condition of a person affects trace element bioavailability.

The study establishes parameters like requirement, basal requirement, and normative requirement that help health policy planners finetune the understanding of the elements further.

In short, requirement is the lowest continuing level of nutrient intake that, at a specified efficiency of utilisation, will maintain the defined level of nutriture in the individual. Basel requirement is the level of intake required to prevent deficiency-related impairment of health. Normative requirement refers to the level of intake that serves to maintain a level of tissue storage or other reserve that is judged by the Expert Consultation to be desirable.

As said earlier, trace elements have serious implications for health in both deficiency and excess. For instance, take the case of iodine deficiency. That it causes hypothyroidism manifested in mental retardation is common knowledge. Goitre too is a well-known phenomenon known to common people. However, studies conducted on animals have shown far-reaching implications of its deficiency. Some of them retarded the growth of foetus and led to still-birth, abortion, and hairless offspring.

The study also takes into account the growing environmental concentration of elements like aluminium, lead, and mercury in the industrial age. "Exposure to aluminium increased markedly as its production increased rapidly in the 20th century. Human exposure to aluminium may also have increased since both the solubility and bioavailability to plants and aquatic life may have increased by acid rain and industrial emission,says the study.

Exposure to several elements has grown tremendously due to industrial activity over the last few decades, thus increasing the chances of toxicity. It is also because of this consideration that the book becomes significant. A must-read for public health officials and policy planners.

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