Quality and sources of food and water consumed by people with chronic kidney disease of unknown etiology in Sri Lanka: a systematic review.

This systematic review explored patterns in (1) sources and quality of the food consumed (2) sources and quality of water consumed (3) nutritional status, and (4) evidence gaps in the literature on the sources and quality of consumed food and water, and nutritional status of people with CKDu in Sri Lanka.

We found that consumed food including rice, other cereals (non-rice), bread, animal source food, eggs, freshwater fish, fruit and vegetables was contaminated with Cd, Pb, As, Mn, Zn, Cu, Fe, Cr, Se, Co, Al, Hg, Sn, K, Na, Mg, Ni, Ca, and V metals. Water sources including wells (dug wells, deep wells, ground wells, and tube wells), pipe water, rivers, tanks, reservoirs, irrigation canals, streams and natural springs were reported as contaminated with Cd, As, Pb, Mn, Cu, Fe, Zn, Ni, Cr, Al, Se, Co, Sr, U, Rb, Mo, Li, Ba, V, B, Hg, Sn, Sb, K, Na, K, Mg, Ca, Ti, and Si metals. Given the high percentage of contaminants, the impact of agrochemicals and fertilizers in CKDu development should be further researched. Rice and vegetables cultivated in the study areas were found to be contaminated with nephrotoxic heavy metals [14, 15, 24]. Inland fish consumed by the people in the study areas were found to be contaminated with heavy metals such as Cd and this was associated with the CKDu prevalence rate [14].

The water sources investigated in the study areas were contaminated with heavy metals, agrochemicals, fertilizers, herbicides, glyphosate, and AMPA [1, 15, 49]. The recommended levels of these contaminants were exceeded in these water sources, thus posing a high risk for human health [1, 11]. Fluoride levels were also significantly high in some water sources which might be correlated with CKDu in some study areas. High levels of physicochemical properties of water sources also pose health risk [11, 51].

Similar to Sri Lanka, CKDu prevalence is increasing in other South Asian developing countries like India, Bangladesh, Pakistan, Nepal, Bhutan, and Afghanistan [66]. A significant impact on kidney diseases in these countries is caused by environmental pollutants such as heavy metals in the environment leading to increased human exposure due to variety of factors such as contaminated air, drinking water and food [67]. Studies conducted in countries like China, Bangladesh, and Taiwan exploring the positive association between dietary As exposure and estimated GFR (eGFR) support the findings of the current review [68,69,70,71]. While Mn, Co, Se, Mo, Pb, and Hg pose health risks to humans, they have also been linked to other diseases such as diabetes, anemia, and to underweight [72]. Modifiable lifestyle factors that are associated with protection from CKD include plant-based diets, sodium restriction, Mediterranean diet, while an increase in risk was reported for dietary Cd intake, red meat, high dietary acid load, high protein diet, and obesity or high BMI [73].

Rice varieties with low Cd concentrations as well as the best fields for paddy cultivation must be identified, and farmers must be educated on measures that reduce Cd concentration in rice and other food [15]. Polished rice is recommended for consumption among vulnerable populations as polishing has been shown to reduce Cd levels [15]. These findings could be applied to the Sri Lankan context to reduce the risk of developing CKDu.

According to quality assessment of the 57 studies included in this review, future studies should focus on justifying the sample size and specifying the inclusion and exclusion criteria in order to improve the methodological quality. Recruitment from the same population will help to reduce the bias in sample selection and increase the methodological quality. However, in almost all the studies, the authors explained the research question or objective clearly and clearly defined and specified the study population. Different exposure levels related to outcome measures were assessed in these studies. Although exposure and outcome measures were clearly defined, valid and reliable in about 50% of the studies, more attention should be paid to further improve the quality of the studies. These quality issues should be considered before generalizing the findings to the population. Future studies are expected to address these limitations, focusing also on recall bias, lack of adjustment for confounders, small sample size, absence of sample size justification, outcome measures, correct measure of the exposures of interests, timeframes, and follow-up.

Future research should include in-depth studies on the impact of glyphosate and AMPA in water and soil on CKDu, on physicochemical properties of water such as hardness, DOC, and should explore the association of nutritional status with the risk of developing CKD.

The current systematic review also has further limitations to acknowledge. The language of the review was limited to English. This may have excluded some publications written in Sinhalese and Tamil, the local languages in Sri Lanka.

In conclusion, this systematic review indicates a higher-level contamination of nephrotoxic heavy metals in the food consumed by people with CKDu in Sri Lanka. Higher levels of Pb, a nephrotoxic heavy metal, were detected in the water sources compared to levels in the consumed food. In addition, high levels of Na⁺ were also found in the studied water sources and highlighted high fluoride levels in water sources consumed by people with CKDu in Sri Lanka. Appropriate strategies to reduce the contamination of heavy metals, agrochemicals, and major ions that reduce the quality of water and food should be implemented to decrease the burden of CKDu in Sri Lanka.