Dietary Cadmium

To estimate dietary Cd, we carried out a search of composition tables reporting Cd levels in food, based on the Total Diet Study (TDS) methodology, which consists of reporting concentrations of contaminants in food [18]. As Mexico lacks such tables, we used tables from the United States, The European Food Safety Authority, Australia, Hong Kong, and Canada. We also used available Cd concentrations measured in selected meat products (ham, sausage, and chorizo) by a study in Mexico City [19]. Each food and beverage item in our FFQ was matched with each of the items found in the Cd composition tables of the di fferent countries. We used the composition tables to obtain an average Cd concentration for each food item, i.e., when the food item was included in all five tables, the average Cd concentration from the tables was used, and so on, if the food item was included in only one table that value was used. In some cases, more than one food item was inquired as the same item on our FFQ (e.g., "broccoli and cauliflower"); for those cases, we used the average Cd for each of the food items from the composition tables. Cd from dishes and prepared foods was estimated (per 100 g of preparation) using a standardized method that accounts for grams of each ingredient in the recipe. Cd levels were estimated in μg/day and were reported for each study visit, as well as the "top ten" foods that contribute the most to the Cd intake according to their frequency of consumption.

We also created a dichotomous variable for children's Cd exposure at each study visit according to the European Food Safety Authority TWI for Cd of 2.5 μg/kg body weight. If the child's Cd intake was above the TWI: High = 1, or below the TWI: Low = 0 [20]. Finally, to account for approximate cumulative Cd exposure, we generated an ordinal Cd score by adding the Cd TWI high or low from all study visits (scores ranged from 0 = low exposure in all study visits, to 5 = high exposure in all study visits). This was done only for children who had dietary information for all five study visits (*n* = 182).

#### *2.3. Kidney Function Parameters*

Kidney function parameters were determined at 9 years by standardized and trained sta ff in the Nutrition and Bio-programming Research, and the Immunochemistry department's laboratories at INPer. Fasting blood samples were collected in BD Vacutainer tubes, and serum was separated according to the standard protocol and stored at −70 ◦C until the analysis. The laboratory analyses were carried out using the following methods:

*Serum creatinine (SCr)* was measured through the kinetic test without deproteinization according to the Ja ffé method [21]. *Cystatin C (Cys C)* was measured by Quantikine Human Cystatin C enzyme-linked immunosorbent assay. *Blood urea nitrogen* (*BUN)* was calculated with the following formula: Serum urea (mg/dL)/2.14; serum urea was determined through the Urease—GLDH test: Enzymatic UV test [22]. *Estimated glomerular filtration rate* (*eGFR)* was calculated using two formulae: (1) Schwartz formula: eGFRSchwartz = (*k* × height)/SCr, where *k* is 0.55 for children under 13 years, height is measured in cm, and SCr is in mg/dL [23]; and (2) the 2012 Cystatin C-based equation: eGFRCystatin C = 70.69 × (CysC)−0.931, where cystatin C is in mg/<sup>L</sup> [24].
