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Veröffentlichungen • Zinc status in pregnancy assessed by hair analysis - nutritional influences

U. Heins, C. Koebnick, C. Leitzmann
Poster for the 10th International Symposium on Trace Elements in Man and Animal, Evian, France 1999

babies

Introduction

A reduction of meat consumption is recommended internationally to prevent nutrition-related diseases (1,2). However, meat is an important nutritional source of zinc in western diets. In western countries serious zinc malnutrition is found rarely but marginal lack of zinc seems to be more spread than assumed up to now. An adequate supply with zinc in pregnancy is necessary for fetal growth and development (3).

Objective

To investigate the zinc status of pregnant women following recommendations for an overall healthy diet, Wholesome Nutrition (WN), in comparison to an average mixed diet.

Method

evian-z0.GIF
Figure 1: Analysis of zinc concentration in scalp hair
(Modified method according to Mc Kenzie 1987)

Pregnant women adhering to WN for about 2 years (preference of foods of plant origin, ovo-lacto-vegetarian diet or low-meat diet - up to two portions of meat per week; little processing of food e.g. whole grain products) (n=56) were compared to women practising an average western diet (control group, CG, n=32). Data were collected in each trimester (9th to 12th, 20th to 22th and 36th to 38th week of pregnancy). The nutritional zinc intake was assessed by an estimated dietary food record (3 x 4 d, Sunday to Wednesday) and calculated with the German Food Code and Nutrition Data Base (Bundeslebensmittelschlüssel BLS II.2).
For the assessment of zinc status in each trimester scalp hair was washed with solutions of Triton-X and EDTA to eliminate contaminations and dissolved in concentrated HNO3 (figure 1). Zinc concentration was analysed by atomic absorption spectrophotometry (4). Furthermore blood samples were taken to analyse zink concentrations and the activity of alkaline phosphatase in serum. For statistical analyses Mann-Whitney´s U-Test and Wilcoxons Signed-Tank test were performed. The concentration of zinc in serum and alkaline phosphatase activity show no differences between the groups (figure 3 and 4). Zinc concentration in hair decreases during pregnancy for both study groups (WN: p<0.0001 and CG: p=0.003), respectively. In all three trimester the WN group show higher zinc concentrations in hair (3.4, 3.0 and 2.4 µmol/g) than the CG (2.9, 2.9 and 2.1 µmol/g) (p=0.002) (figure 5).

Results

The nutrient density of zinc is higher in the WN group [1,5 mg/MJ (1.3/1.6)] than in the control group [1,3 mg/MJ (1.2/1.5)] (p=0.001). The absolute intake of zinc (~12.4 mg/d) show no difference between WN and CG. WN get less zinc from meat, fish and eggs (p<0.0001) but more from whole grain products (p<0.0001) than CG. About 30 % of the zinc intake by WN derives from whole grain products, only 7 % from products from refined flour and 5 % from meat, fish and eggs. Only 10 % of the zinc eaten by CG comes from whole grain products, 19 % from refined flour products and 27 % from meat, fish and eggs (figure 2).

Discussion

The concentration of zinc in serum declines during pregnancy mainly caused by plasma dilution. The activity of the alkaline phosphatase increases due to placental alkaline phosphatase, which is measurable in the mothers blood from the 16th week of pregnancy (5). Therefore both parameters are limited in their evidence. Hair zinc concentration is not influenced by plasma dilution or placental enzymes, it represents a useful additional analytical material for zinc (6). The supply with zinc for both groups is adequate during pregnancy, while zinc content in hair is higher in WN group than in the CG. This indicates that zinc from WN is better biavailable than zinc from an average western diet. Because of the more favourable zinc status of those consuming more whole grain products (WN) the current discussion of the lower zinc bioavailiability due to phytate cannot be supported (7). More studies are necessary to determine the bioavailiability of whole diets instead of single nutritional factors.

Conclusions

This study shows that a well balanced low-meat or ovo-lacto vegetarian diet during pregnancy may lead to a better supply with zinc.

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 References:

  1. Nutrition Committee, American Heart Association: Dietary guidelines for healthy American adults. A statement for health professionals from the Nutrition Committee, American Heart Association. Circulation 94: 1795-1800, 1996.
  2. World Cancer Research Fund/American Institute for Cancer Research: Food, nutrition and the prevention of cancer: A global perspective. Banta Book Group, Menasha, 1997.
  3. Caulfield LE, Zavaleta N, Shankar AH, Merialdi M: Potential contribution of maternal zinc supplementation during pregnancy to maternal and child survival. Am J Clin Nutr 68 (suppl): 499S-508S, 1998.
  4. Mc Kenzie JM: Alteration of zinc and copper concentration of hair. Am J Clin Nutr 31: 470-476, 1978.
  5. Thomas L: Indikatoren und Bewertung von Laborbefunden für die medizinische Diagnostik. 5. Aufl., TH-Books-Verlag und Gesellschaft Frankfurt, 1998.
  6. Folin M, Contiero E, Vaselli GM: Trace element determination in humans. The use of blood and hair. Biol Trace Elem Res 31: 147-158, 1991.
  7. Sandström B: Bioavailability of zinc. Eur J Clin Nutr 51 (suppl): 17-19, 1997.

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