Fig. 1. Mean plasma total homocysteine concentrations (and 95% confidence intervals) by quintile of plasma folate (left) and vitamin B₁₂ (right) in women from Puriscal, Costa Rica. Means are adjusted to an age of 40 years. Asterisks indicate significant difference from the mean in the highest quintile (** p < 0.01; *** p < 0.001).