Assessment of Consumers’ Exposure to Vegetable Dietary Nitrate in Katima Mulilo, Namibia

Abstract

Leafy vegetables occupy a very important place in the human diet, but unfortunately constitute a group of foods which account for high dietary nitrate ingestion by human beings. Samples of spinach, rapes, kale chomolia, chomolia, 5-years, and cabbage highly traded in Katima Mulilo Open market were purchased directly from farmers and analysed for consumers' nitrate exposure. Samples were prepared for laboratory analysis using the in-house method LPFC-126 of the Health Protection Branch Laboratories, Bureau of Chemical Safety. Aqueous extracts of the vegetable sample were anaylsed for nitrate concentrations using MERCK reflectometer (RQflex) and each result reported in mg/kg. The concentrations of nitrate in the vegetables varied widely between 644.30 to 6,463.37 mg/kg wet weight basis. The vegetable consumption survey of 400 participants in the study area indicated that 58% of adult male and 60% of adult female (> 18 years) consumed 5-years as their preferred leafy vegetable while that of the children (12 - 17 years) showed 40% male and 57% female. Dietary nitrate exposures of the consumers via ingestion of these vegetables showed that 5- years recorded the highest mean level of 30.98 mg NO3 - /day body weight while cabbage recorded the least (0.21 mg NO3 - /day body weight). Generally, the levels of the vegetable dietary nitrate exposures obtained in this study are below the reported international estimates of intakes from food which varied between 31-185 mg NO3 - /day in Europe and ≈ 40-100 mg NO3 - /day in the United States. However, the bioavailability of dietary nitrate is 100% and this has implication for ingestion from a high nitrate diet source such as the 5-years vegetable. Therefore, producers' efforts should target a reduction in nitrate contents as this will add value to vegetable diets already very popular for their nutritional and therapeutic properties. This will involve among others, adopting appropriate strategies to determine the role of individual physiological factors and agronomic practices in the process of nitrate accumulations in vegetables in the study area.