percent—a larger percentage than was found for males and nonpregnant women (Chong and Ho, 1970).

Oldham and coworkers (1950) found a very strong correlation (r = 0.98) between total thiamin intake and excretion but no consistent decrease in thiamin excretion or in the percentage of a test dose excreted over the course of pregnancy. These investigators compared their results with those from studies of nonpregnant women of comparable ages (Daum et al., 1948; Hathaway and Strom, 1946; Oldham et al., 1946) and found that the pregnant women excreted two to three times as much thiamin as did the nonpregnant women on similar intakes (estimated at less than 1 mg) whereas their excretion of a test dose was similar. In contrast, Toverud (1940) observed no or minimal excretion of thiamin in the urine normally or after a load test in 46 percent of 114 pregnant women. Lockhart and coworkers (1943) reported that approximately three times as much thiamin, as obtained from both supplements and diet, was needed by 16 pregnant women to achieve the urinary excretion peak in the tenth lunar month as was needed by a group of nonpregnant women.

For pregnancy the requirement is increased by about 30 percent based on increased growth in maternal and fetal compartments (approximately 20 percent) and a small increase in energy utilization (about 10 percent). This results in an additional requirement for pregnancy of 0.27 ≅ 0.3 mg/day of thiamin. Data from the studies cited above are equivocal about the effects of pregnancy on thiamin requirements and thus are not useful in refining this estimate. Adding 0.3 to the EAR of 0.9 mg for nonpregnant, nonlactating women gives an EAR for the second and third trimesters of pregnancy of 1.2 mg. No adjustment is made for the woman’s age.

The RDA for thiamin is set by assuming a coefficient of variation (CV) of 10 percent (see Chapter 1) because information is not available on the standard deviation of the requirement for thiamin; the RDA is defined as equal to the EAR plus twice the CV to cover the needs of 97 to 98 percent of the individuals in the group (therefore, for thiamin the RDA is 120 percent of the EAR).