Study design and sample size calculation
blisters
The study had a randomized, double-blind, placebo-controlled crossover design with two 5-week periods separated by a 5 week interim washout period. In each period, to standardise the experimental conditions, one capsule (DHA-supplement or placebo) per day was taken by the participants with one of their main meals, because high DHA absorption is expected when consumed with meals [The capsules were delivered in blisters packed in a white box and neither the participants nor the researchers knew the type of capsule given to each participant. The experimental period was established according to the recommendations of the human trials on lipids which was at least 4 weeks [The volunteers were randomly assigned the DHA treatment or placebo with the Microsoft Excel randomization function (RAND). Participants were allocated to one sequence starting with DHA-supplement and then placebo, or starting with placebo and then DHA-supplement. However, there were a few cases were volunteers who lived together were provided with the same capsule type to avoid mixing capsules and improve adherence.The statistical power was set at 85% and the confidence level at 95%. Taking serum DHA as the main variable and knowing its variability obtained in our previous study performed in similar vegetarians [