Age and sex are important factors in determining normal retinol levels

Cut-off levels for serum retinol levels of 20 micrograms/dl for marginal and 10 micrograms/dl for definite deficiency have been advocated and extensively used in population studies. However, the blood serum levels of retinol of the newborn are known to be very low and although the age dependency of the retinol binding protein has been described, the normal levels of serum retinol at different ages have not been reported from larger series. While studying poor populations of young infants in Lahore, Pakistan, we thought it necessary to try to achieve appropriate reference values by analysing the levels of serum retinol of expatriates from the Indian subcontinent who live in the affluent United Arab Emirates, where retinol deficiency is not seen either at the hospital or the community levels. We have studied material, cord blood, infantile and adult levels of retinol and found a highly significant age relationship of serum retinol levels. During very early infancy the 'normal' mean is below what has been considered deficiency. This is new information and important in the evaluation of retinol status of individuals as well as populations. In addition, we found lower levels in women, pregnant or non-pregnant, than those in adult men. This sex difference in adults was not seen in infants. We recommend a cut off level for deficiency of 10 micrograms/dl, but only for those above 1 month of postnatal age.