Levels of retinol, beta-carotene, and alpha-tocopherol were determined in the serum of 415 adults over age 35 years who had volunteered in 1974 to donate blood for cancer research in Washington County, Maryland. Males had higher levels of serum retinol, lower levels of beta-carotene, and only slightly lower levels of alpha-tocopherol than did females. No clear-cut association was noted with age. Smokers had decreased serum levels of beta-carotene. Vitamin supplementation was associated with higher serum levels. Persons taking medication for high blood pressure had higher levels of retinol and alpha-tocopherol, but lower levels of beta-carotene.
The influence of high dose intake of ascorbic acid on the urinary excretion of oxalate was investigated in five healthy male volunteers. Oxalate was measured by a newly developed specific method using isotachophoresis. With intakes of 10 g ascorbic acid (5 X 2 g daily for 5 days; four subjects) mean urinary oxalate excretion was enhanced from about 50 mg to 87 mg (range 60 to 126 mg) per day. At least 25% of the ascorbic acid was absorbed and excreted with the urine. On discontinuing ascorbic acid administration, oxalate excretion returned to baseline values within 24 h. The time-course of oxalate excretion revealed that following the 3rd dose of 2 g ascorbic acid a plateau in urinary oxalate excretion was reached (0.6 microgram ml-1 min-1) which was not exceeded despite additional 2-g doses of ascorbic acid. On termination of ascorbic acid administration the oxalate excretion rate remained at this level for a further 6 h and then decreased to prestudy rates. No effect of high-dose ascorbic acid ingestion was found on the daily urinary excretion of creatinine, uric acid, and inorganic phosphate. Calcium excretion was slightly reduced. In comparison to the large amounts of ascorbic acid ingested, the increase in urinary oxalate excretion as measured by isotachophoresis in these healthy male volunteers was very low, and is thus similar to the change in urinary content of oxalate which results from consuming normal diets.
From 610 blood samples collected in September 1983 in an intervention trial in Huixian, Henan Province, People's Republic of China, which were individually analyzed for retinol, beta-carotene, and alpha-tocopherol levels, 10 pools were formed from 50 individual samples, and the vitamin levels in the merged pools were also measured. Oxidation losses by repeated thawing and refreezing render the absolute levels measured in the pools smaller than the corresponding means of the individual measurements. A very good relative agreement was found between pool levels of retinol and beta-carotene and the respective means. The pooling technique could be a valuable tool in large correlation studies and has possible further applications in case-control studies.
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