Effect of blood vitamin A levels on the dark adaptation of mineworkers.

: The average dark adaptation time for newly recruited Black mineworkers is longer than that reported for Whites. While this longer dark adaptation time may result from a number of pathological conditions, its most likely cause is a deficiency of vitamin A in the diet. A study was conducted in which the vitamin A level of the blood and the dark adaptation times were correlated in a group of Black mineworkers upon arrival and again after 4 - 6 months continuous work underground in a gold mine. The study indicated that a very marked decrease occurred in the miners' serum vitamin A level between the time of arrival at the mine and the second examination. This difference was found to be highly significant. This decrease was accompanied by an increase in mean dark adaptation time, which was significant at the 5% level. These observations accord with the findings of a previous study and are indicative of an inadequate dietary intake of vitamin A during the period when the miners were on the mine diet.