The MING study was a cross-sectional study designed to investigate the dietary and nutritional status of pregnant women, lactating mothers and young children aged from birth up to three years living in urban areas of China conducted in 2011 and 2012. Eight cities were chosen for the MING study according to the geographical location and status of economic development defined as first or second tier cities. The 8 cities included 4 first tier cities: Beijing, Shanghai, Chengdu and Guangzhou and 4 s-tier cities: Shenyang, Lanzhou, Zhengzhou and Suzhou. In each city, two maternal and child care centres (MCCC) were randomly selected. The MCCC is the primary health care facility that provides free birth-related health services to all women and their young children in all regions of China. The care centres are located in local residence communities in different districts of the city for easy access. The main services of MCCCs are to conduct regular heath checks for pregnant women and their babies, and to provide regular vaccinations to young children from birth up to school age. In MCCCs, young children aged 6 to 35 months were randomly selected based on child registration information and their parents or caregivers were approached for subject recruitment. Response rate was 66 %. Exclusion criteria were parents or caregivers with psychopathy or abnormal memory, infants with hereditary disease or disability, as well as infants suffering from respiratory diseases or digestive tract diseases during the investigation. A stratified sample of 1498 young children in three age groups of 6 to 11, 12 to 23 and 24 to 35 months was obtained. Children under 12 months of age are called infants; children 12 to 35 months of age are called toddlers.
The study was conducted according to the guidelines in the Declaration of Helsinki. All of the procedures involving human subjects were approved by the Medical Ethics Research Board of Peking University (No.IRB00001052-11042). Written informed consent was obtained from the primary caregiver of each infant or toddler participating in the study.
Data collection and nutrient database
All information collected from the study was obtained through face-to-face interviews with the parent or caregiver of each child. All interviewers were trained with a standard protocol for conducting the interview. The interview covered the information of a general questionnaire, a single 24-h dietary recall, a food frequency questionnaire, a survey on dietary supplement use and consumption of commercial baby food products.
The general questionnaire provided information on family demographic and socioeconomic characteristics, such as age, birth weight, recent medical history, education and occupation of parents and monthly household income (per capita). Information about feeding practices was also collected through this questionnaire. One 24-h dietary recall was completed for all infants and toddlers. Interviewers asked the primary care-giver about all foods, beverages and supplements that the infant or toddler consumed on the previous day. A picture booklet of common foods consumed in China and measurement aids such as spoons, cups and bowls were used to estimate the amount of foods and beverages consumed. Details about food ingredients of homemade foods or meals eaten out were also asked and recorded. In addition, information on the use of dietary supplements was collected, including the name and brand of the supplement, age when supplement was first given and the amount used. A list of dietary supplements commonly used in China was used to identify the supplements reported during the interview.
All the questionnaires including the 24-h dietary recalls were reviewed by the project supervisors in each of the cities for missing foods and unrealistic quantities reported. When such issues were found, the caregiver was contacted by telephone to verify the information. Of 1498 dietary records, 89 records (6 %) could not be verified were excluded from the final data analysis. Thus, final samples sizes of the subgroups were 444 children 6 to 11 months, 476 children 12 to 23 months and 489 children 24 to 35 months.
Food records were entered and processed with a food composition database created for this study that included data from Chinese Food Composition (CFC) tables 2004 & 2009 [12, 13] and branded-products and supplements from China. CFC contains information of 1773 foods with 36 nutrients. The values for both beta-carotene and retinol were available in the database, thus vitamin A was estimated in retinol activity equivalents using the following formula : Retinol activity equivalents = μg retinol + 1/2 (μg beta-carotene equivalents/6).
In the CFC, the vitamin A concentration for breast milk was 11μgRE/100 g, which is significantly lower than our analysis of the breast milk samples from the MING study, 70 μgRE/100 g (unpublished data). This MING value is in line with the vitamin A concentration of breast milk reported by USDA , therefore, this value was used to estimate vitamin A intake from breast milk. In addition, in CFC, vitamin B6 data of breast milk was not available; we also used our analysis for vitamin B6 calculated from breast milk.
Additionally, data on infant products was limited in CFC, therefore, we compiled nutrient information for 78 branded-food products, including baby food and infant formula products using nutrition information from product labels. When a specific food was reported for which there was no nutrition information available, the nutrient data for a similar product was used. Finally we also compiled nutritional information from 75 dietary supplements sold in China.
The amount of breast milk consumed was estimated, using the approach developed by Butte et.al. Data on the amount of human milk fed was not collected, but rather data was collected on the number of times the mother nursed during the day. For infants aged 6 to 11 months fed human milk as the sole milk source, the amount of human milk was assumed to be 600 mL/day; for partially breastfed infants, the amount of human milk was estimated as 600 mL/day minus the amount of formula/other milks consumed. For breastfed toddlers aged 12 to 23 months, the amount of human milk was estimated as 89 mL per feeding occasion; and for toddlers aged 24–36 months, the amount of human milk was estimated as 59 mL per feeding occasion .
All statistical analyses were performed using SAS version 9.2 (SAS Institute, Inc., Cary, NC, USA). Nutrient adequacy was assessed by comparing nutrient intakes to the Recommended Dietary Intake from the Chinese Nutrition Society 2013 . The nutrient intakes, including the nutrients from food, beverages and dietary supplements are reported for each of three age groups: infants, younger toddlers and older toddlers. Since only one day 24-h recall was available for our sample, we were not able to adjust the distribution of nutrient intake to reflect usual intake as can be done with multiple days of dietary intake. Nutrient intake assessments were done by comparing mean intakes with the Adequate Intake (AI). A population group with a mean nutrient intake at or above the AI can be assumed to have nutritionally adequate diets and implies a low prevalence of inadequate intakes . Estimated Average Requirement (EAR) is also presented for reference and discussion. The energy requirements are expressed in terms of estimated energy requirements (EER). The EER is defined as the sum of the energy intake predicted to maintain energy balance for an individual’s age and weight, as well as an allowance for energy deposition to account for growth .