Schooling et al. BMC Public Health 2011, 11:345 http://www.biomedcentral.com/1471-2458/11/345 inflammation among men may be due to obesity [9]. In a large sample from the developing country setting of south- ern China, we examined whether a marker of childhood nutrition, positively associated with cognition [27], but sex-specifically associated with central obesity and some lipids [28], also had sex-specific associations with inflam- matory markers. Methods Sources of data The Guangzhou Biobank Cohort Study is a collaboration between the Guangzhou No. 12 Hospital, the Universities of Hong Kong and Birmingham, and has been described in detail [29]. Recruitment of participants draws from “The Guangzhou Health and Happiness Association for the Respectable Elders”, a community social and welfare association unofficially aligned with the municipal govern- ment where membership is open to anyone aged 50 years or older for a monthly, nominal fee of 4 Yuan (50 US cents). Recruitment for phase 3 took place from Septem- ber 2006 to January 2008. About 7% of permanent Guangzhou residents aged 50 years and over are members of “The Guangzhou Health and Happiness Association for the Respectable Elders”, of whom 11% enrolled for phase 3 recruitment, and were included if they were capable of consenting, ambulatory, and not receiving treatment mod- alities which if omitted may result in immediate life threa- tening risk, such as chemotherapy or radiotherapy for cancer, or dialysis for renal failure. Participants underwent a half-day detailed medical interview, including disease history, and physical examination. The Guangzhou Medi- cal Ethics Committee of the Chinese Medical Association approved the study and all participants gave written, informed consent before participation. The detailed methods of measurement have been reported [29]. In brief, standing height was measured with- out shoes to the nearest 0.1 centimeter. Sitting height was measured with the participants sitting on a standard stool; leg length was calculated as the difference between height and sitting height. Weight was measured in light clothing to the nearest 0.1 kilogram. Hip circumference was mea- sured at the greatest circumference round the buttocks below the iliac crest. Waist circumference was measured horizontally around the smallest circumference between the ribs and iliac crest, or at the level of the navel for obese participants. Quantitative haematological analysis was performed using a SYSMEX KX-21 haematology ana- lyzer, from which white blood cell counts, lymphocyte and granulocyte counts were available. Exposure assessment In developing countries long running cohort studies that could provide life long measures are not available, poten- tially precluding valuable evidence from such settings in Page 2 of 6 the foreseeable future. Instead, in this study childhood nutrition was assessed from a simple question about a notable aspect of childhood nutrition, i.e., meat eating, because this cohort grew up in era and setting where meat consumption was relatively low, highly valued and not constrained by religious beliefs. Recalled childhood meat eating was ascertained by asking participants whether they ate meat as a child with answers in Chinese which translate as “never”, “about once a year”, “about once a month”, “about once a week” or “almost daily”. Few (<1%) reported “never” eating meat in childhood, and both “about once a year” and “about once a month” represent occasional meat eating, so we created a 3 point scale: “</1 week”, “about once a week” and “almost daily”. We cannot validate recalled childhood meat eating against actual childhood intake or maternal recall given the age of our participants. However, we have previously shown that recalled childhood meat eating does have the expected negative association with age of menarche and positive associations with height and childhood socio- economic position [27,28]. Moreover, in other contexts, recalled dietary intake from adolescence has been shown to have some reproducibility and validity [30]. Outcome measure White blood cell count was considered, as in other studies, as a marker of a pro-inflammatory state [4], and less well functioning immune system. As we do not have a detailed breakdown of different white blood cell types, such as macrophages, we also considered granulocyte and lympho- cyte counts as outcomes because these immune cell sub- populations largely relate to innate and adaptive immunity respectively. They have previously been used as markers of inflammation [31,32]. Sex-steroids may also have differen- tial effects on immune cell sub-populations [20,33]. Statistical analysis Multivariable regression was used to assess the adjusted association of recalled childhood meat eating with total white blood cell count and its differentials. We examined whether the outcomes had different associations with recalled childhood meat eating by sex or age from the heterogeneity across strata and model fit assessed from the Akaike Information Criterion for models with and without the relevant interaction term. We also included in the model all other interactions of sex or age, as appropriate, with other confounders that contributed to model fit. Potential confounders considered were age (5 year age- groups), sex (if appropriate), socio economic position at three life stages (based on parental possession of three relevant items (watch, bicycle and sewing machine) in childhood [10], education and longest held occupation), measures of early life living conditions (leg length and