American Journal of Clinical Nutrition, Vol. 70, No. 1, 112-113,
July 1999
© 1999 American Society for Clinical Nutrition
Reply to NW Solomons et al
Ann F Walker
Hugh Sinclair Unit of Human Nutrition Department of Food Science and Technology The University of Reading Reading RG6 6AP United Kingdom E-mail: a.f.walker{at}afnovell.reading.ac.uk
Dear Sir:
I am pleased that our paper (1) highlighted the need to address all potential micronutrient deficiencies in future studies of zinc intervention. Because zinc is an integral part of so many enzymes, the activity of which is dependent on the presence of a range of micronutrients, it would not be surprising to find that the full nutrient potential of zinc is realized only when these micronutrients are adequately supplied in the diet.
With regard to multinutrient interventions, one nutrient that has received little attention is magnesium, which is likely to be low in the refined diets of many children in developing countries. I emphasize magnesium because its nutrition has many characteristics in common with that of zinc (eg, lack of body stores, multiplicity of roles, and growth cessation as an adaptive response to deficiency). Unfortunately, the relevancy of magnesium deficiency to human health is often overlooked. This is despite the fact that in most dietary surveys of those eating refined diets, as exemplified by the UK National Diet and Nutrition Survey (2, 3), magnesium emerges at the top of the list of nutrients for which persons (often the majority) in all age groups fail to reach dietary targets. It was reassuring that 100 mg Mg was included in the micronutrient supplement administered daily to both the zinc-supplemented and placebo groups of children in the Guatemalan study (4). This inclusion was unusual because magnesium is usually excluded from multinutrient supplements on the grounds that a meaningful daily supplement of the mineral would make the formulation too large to swallow in a once-daily tablet.
As Solomons et al indicate in their letter, the results of our study provide a possible explanation for the variable growth responses to zinc supplementation seen in previous studies of children. This now needs to be followed up with studies designed specifically to test the hypothesis that a full growth response to zinc occurs only in a state of repletion of other micronutrients. Dissecting the role of magnesium in the zinc growth response would be particularly interesting. Once a clear picture emerges for growth, other responses of zinc repletion could be examined similarly, including the immune response. I welcome the letter from Solomons et al and fully agree that our study further emphasizes the notion that a cautious approach should be taken to the use of single-mineral supplements in public health programs.
REFERENCES
-
Kikafunda JK, Walker AF, Allan EF, Tumwine JK. Effect of zinc supplementation on growth and body composition of Ugandan preschool children: a randomized, controlled, intervention trial. Am J Clin Nutr 1998;68:1261–6.[Abstract]
-
Finch S, Doyle W, Lowe C, et al. National Diet and Nutrition Survey: people aged 65 years and over. Vol 1. Report of the Diet and Nutrition Survey. London: Her Majesty's Stationery Office, 1998.
-
Gregory J, Collins DL, Davies PSW, Hughes JM, Clarke PC. The dietary and nutrition survey of British adults. Office of Population Census and Surveys. London: Her Majesty's Stationery Office, 1990.
-
Cavan KR, Gibson RS, Grazioso CF, Isalgue AM, Ruz M, Solomons NW. Growth and body composition of periurban Guatamalan children in relation to zinc status: a longitudinal zinc intervention trial. Am J Clin Nutr 1993;57:344–42.[Abstract/Free Full Text]
