In the 6th revision of the Japanese Recommended Dietary Allowance (RDA)-Dietary Reference Intakes (DRI)-the RDA of folate was stated to be 200μg/day for an adult, all of which can be obtained from food. However, as evidence-based knowledge on this subject is insufficient, there is an obvious need for new data, collected by us in Japan, to be considered. To study the dietary requirement of folate, a group of healthy adults comprising 10 men and 10 women were fed a semi-purified diet following the Japanese RDA. In the women, the serum level and urinary excretion of folic acid were increased for the 8 days of the experiment. On the other hand, in the men, a decrease in the urinary excretion of folic acid was observed during the experimental period, but no change was noted in the serum level of folic acid. There was a sex difference in the dietary requirement of folic acid. These findings suggest that the 200μ/day intake used in this study would be adequate for maintaining a constant serum level of folic acid in women, but that a deficiency of folic acid might occur in this situation in men.

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DNA microarray technology was used to evaluate the effect of dietary intake of nigana (Crepidiastrum lanceolatum), an edible plant in Okinawa, on gene-expression pattern in the liver. The expression levels of several genes were changed in the liver of mice that consumed nigana or spinach. Whereas dietary intake of spinach and water did not affect the mRNA level of erythropoietin (EPO), intake of nigana induced gene expression of EPO in the mouse liver. To produce high-quality vegetables, we changed the growth conditions for nigana. Three irrigation rates (potential free energy; pF 1.5, 1.8, and 3.0) were used for nigana hydro culture. The irrigation conditions affected the contents of nutritional factors in nigana as well as the level of expression of the EPO gene in the liver of mice that ingested the plant. The pF 1.5 condition did not afford the highest levels of nutrients. However, the low levels of potassium and nitric acid found under this condition were a positive aspect, as these chemicals are known to be unfavorable factors in vegetables. The greatest induction of EPO mRNA at pF 1.5 was also beneficial. These findings indicate that the application of DNA microarray technology to experimental animals ingesting a specific dietary component is useful for producing high-quality food.

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Human studies differ from studies using experimental animals or cells because of differences in not only purpose but also research methods, resulting in different reporting styles. This brief lecture discusses some points necessary to consider when human studies are planned, conducted, and reported. It focuses especially on ‘basic characteristics of the subjects’, ‘confounding factors’, ‘number of subjects’, ‘measurement errors and statistical significance’, ‘study limitation’, and ‘population representativeness’. Based on this knowledge, it summarizes the points necessary for writing scientific articles on human studies. However, this lecture does not deal with studies, even with humans, conducted in a laboratory where strict control of the subjects is possible, but includes studies using humans in more or less free living conditions, to which epidemiologic methodology is generally applied. Epidemiologic studies are divided into observational studies and interventional studies. Observational studies are then divided into descriptive epidemiology and analytical epidemiology. The latter is mainly discussed here with short comments on interventional studies.

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