Effect of nitrite ingestion on the bioavailability of folate in the rat.

The effect of nitrite ingestion on the intestinal deconjugation and absorption of folic acid (PGA) and brewers yeast folate was investigated using a rat bioassay and liver folate uptake as the response parameter. Male weanling Sprague Dawley rats were depleted on a low folate AIN-76A formulated basal diet for 21 days. During a 14 day repletion period, folic acid (PGA) and brewers yeast were added to provide 0.25, 0.5 and 1.0 mg of folate per kg of diet. Potassium nitrite was administered as part of the diet at 0.5%. All diets were made isonitrogenous and isocaloric. Based on a parallel line assay, the relative bioavailability of folate in the brewers yeast diet (109) was significantly higher than in the standard diet (PGA = 100). When combined with nitrite, the relative bioavailability of the PGA diet was not significantly different (101), while that of the brewers yeast diet was significantly lower than the standard diet. Concomitant ingestion of nitrite significantly reduced the bioavailability of brewers yeast folate but not that of PGA in rats. This appeared to be a direct effect of oxidation by nitrite on the more susceptible substituted folates in brewers yeast.

Bioavailability of folate following ingestion of cholestyramine in the rat.

The effect of cholestyramine ingestion on the intestinal deconjugation and absorption of folic acid (PGA) and brewers yeast folate was investigated using a rat bioassay and liver folate uptake as the response parameter. Male weanling Sprague Dawley rats were depleted on a low AIN-76A formulated basal diet for 21 days. During a 14 day repletion period folic acid (PGA) and brewers yeast were added to provide 0.25, 0.5 and 1.0 mg of folate per kg of diet. Cholestyramine was administered directly as part of the diet at 1.1%. All diets were made isonitrogenous and isocaloric. Based on a parallel line assay, the relative biological value of folate for PGA + cholestyramine (79) was significantly different from the standard diet (PGA = 100), while those for brewers yeast (88) and for brewers yeast + cholestyramine (88) did not differ from the standard diet. Ingestion of cholestyramine significantly reduced the bioavailability of PGA versus brewers yeast folate in rats.

Folate levels in human liver from autopsies in Canada.

Liver folate is considered to be a direct measure of body folate stores. Specimens of 560 livers were therefore collected during autopsies at hospitals in seven cities across Canada, and analyzed for "total" folate. The values obtained ranged from 2.7 to 15.6 micrograms/g. Stillborn infants had the lowest mean liver folate levels (5.9 microgram/g). Mean liver folate levels tended to increase from birth to a peak between 11 to 30 years (8.8 micrograms/g), and then decreased with increasing age. This trend was reflected in an increased proportion (6 to 15%) of folate levels in the 3.1 to 5.0 microgram/g range in older subjects. Liver folate levels of male subjects did not differ from those of females. Mean liver levels tended to be slightly higher, and the number of liver levels between 3.1 to 5.0 micrograms/g was lower, in subjects dying accidentally (7.8%) and from heart and coronary disease (8.7%), than in those dying from cancer, respiratory diseases or other causes (11.7 to 15.3%). Only two subjects had liver folate levels below 3 microgram/g. In this survey, there was thus little evidence of severe folate deficiency.

Nutrient levels of some foods of Eskimos from Artic Bay, N. W.T., Canada.

Native food samples of caribou, seal, and arctic char were collected from resident Eskimos in Arctic Bay, N.W. T., and analyzed for nutrients. Caribou and seal meats were similar in protein and fat content in comparison with beef. Arctic char was above the average in protein and fat content for fish. Ascorbic acid was present in significant amounts only in baby seal liver. Thiamin, riboflavin, vitamin B12, folacin, and pantothenic acid content ranged from average to high for seal and carbiou meat, respectively, in comparison to published values for pork and beef. The vitamin B6 content of caribou meat was comparable to average values reported for pork and beef but was lower in seal meat. Baby seal liver contained similar levels of thiamin, riboflavin, vitamin B12, folacin, and pantothenic acid and less vitamin B6 than those reported for pork, beef, calf, and lamb liver. Arctic char was not appreciably different in these vitamins from other fish. The iron content of the Eskimo foods was higher than the meat group of the mixed Canadian diet. The macro mineral nutrients in these foods were comparable to those in beef and fish. The amino acid composition of caribou and seal meat was similar to beef, except that seal meat had a lower content of sulfur-containing amino acids and a much higher content of histidine. The sample of seal and arctic char were relatively high in concentrations of long-chain unsaturated fatty acids.

Vitamin A reserves of Canadians.

-A survey of vitamin A and carotene stores of Canadians at five major centres across Canada was completed. Vitamin A and carotene analyses were performed on approximately 100 human liver specimens obtained at necropsy from each location.Age influenced liver vitamin A stores. Children between 1 and 10 years of age had the highest vitamin A stores while a trend toward lower liver stores occurred between 20 and 40 years of age. Females had higher liver carotene stores than males but there was no such difference in vitamin A stores.SUBJECTS FROM ALL LOCATIONS WERE CLASSIFIED ACCORDING TO CAUSE OF DEATH: accidental, heart and coronary artery diseases, cancer, respiratory diseases and a miscellaneous disease group. The mean liver vitamin A and carotene stores of the accidental death group differed only from the cancer group. In contrast to the disease groups, no case with undetectable vitamin A was found in the accidental death group.The mean vitamin A and carotene stores of Vancouver subjects were generally higher than those for the other locations. Montreal showed more values in the 0-40 mug. per g. range than the other locations. Vancouver had the least number (15%), with Halifax, Ottawa and Winnipeg being intermediate (32%). These data suggest the need for improved nutrition, prophylactic treatment in disease states and the need for further research on the utilization and metabolism of vitamin A.