To explore anthropometric indicators and mental development in very-low-income children in the second year of life.

Cross-sectional survey.

Low-income areas (income <20th percentile) in semi-urban Mexico (defined as towns or cities with 2500–50 000 inhabitants).

Eight hundred and ninety-six children aged 12.5–23.5 months surveyed from September to December 2001.

Questionnaire survey and anthropometric survey of households. Multivariate regression models evaluated differences across age in anthropometry (height-for-age Z-score (HAZ) and weight-for-height Z-score) and cognitive function (Mental Development Index (MDI) of the Bayley Scales of Infant Development) while controlling for socio-economic and parental characteristics.

There was a significant decline in HAZ and in age-adjusted MDI score across the second year of life. Although the children showed MDI scores close to the mean, normed US values at 13–14 months, the scores were significantly lower than expected in older children (P < 0.0001), even after controlling for socio-economic status and parental characteristics. At 13–14 months, only 3% of children received scores below 70 (less than minus two standard deviations), whereas by 19–20 months, almost 17% of children were performing below this level. No socio-economic or parental characteristics were significant predictors of HAZ or MDI.

Parallel deficits are evident in both height-for-age and cognitive functioning during the second year of life in low-income Mexican infants. The consistency of these growth and development findings further stresses the need for targeted interventions to reduce the vulnerability of low-income Mexican children very early in life.

To evaluate the validity of a food-frequency questionnaire (FFQ) for assessment of the dietary intakes of polyunsaturated fatty acids (PUFAs) against a biochemical marker of fat intake, erythrocyte cell membrane phospholipid levels, during pregnancy.

Cross-sectional analysis.

Developmental Neurobiology Department, National Institute of Perinatology, Mexico City.

One hundred forty-six healthy pregnant women during the last trimester of pregnancy. Among women enrolled, the first 35 pregnant women (24%) had their erythrocytes analysed for fatty acid status.

We administered an FFQ and compared intakes of PUFAs against their erythrocyte cell membrane concentrations, processed by gas chromatography.

Pearson correlation coefficients among α-linolenic acid (ALN), docosahexaenoic acid (DHA) and eicosapentaenoic acid in erythrocyte cell membranes against their crude dietary counterparts were 0.32, 0.35 and 0.36 (each P < 0.05). In a simple linear regression, erythrocyte DHA and arachidonic acid (AA) were significantly related to their respective dietary intakes (β = 0.30, 95% confidence interval (CI): 0.007–0.60, P = 0.045 for DHA; β = 0.49, 95% CI: 0.010–0.98, P = 0.044 for AA). Erythrocyte cell membrane ALN concentration (%/total) was only marginally related to ALN dietary intake (mg day−1) (β = 0.52, 95% CI: −0.020–1.10, P = 0.061). However, after adjustment for long-chain n–3 PUFA/AA, this association reached significance (β = 0.44, 95% CI: 0.026–0.825, P = 0.038). Main dietary sources for n–3 PUFAs were canned tuna fish and fresh catfish; for n–6 these were eggs and cow's milk. The use of this FFQ in these pregnant Mexican women provided estimates of average long-term intakes of PUFAs and correlated reasonably well with their erythrocyte cell membrane phospholipid status. However, we need to consider that, during pregnancy, there is a faster turnover of PUFAs from fat storage that may modify the profile of erythrocyte PUFAs and lower the correlation between dietary intake and erythrocyte PUFAs.