What test can be used to assess whether mean serum retinol has increased over 3 years among subjects in the vitamin A group? 

Ophthalmology

A 5-year study among 601 participants with retinitis pigmentosa assessed the effects of high-dose vitamin A (15,000 IU per day) and vitamin E (400 IU per day) on the course of their disease. One issue is to what extent supplementation with vitamin A affected their serum-retinol levels. The serum-retinol data in Table 10.31 were obtained over 3 years of follow-up among 73 males taking 15,000 IU/day of vitamin A (vitamin A group) and among 57 males taking 75 IU/day of vitamin A (the trace group; this is a negligible amount compared with usual dietary intake of 3000 IU/day).

Table 10.31 Effect of vitamin A supplementation on serum-retinol levels

 

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Year 0 Year 3 Retinol (mmol/L) Vitamin A group Trace group Mean + sd Mean + sd 73 1.89 + 0.36 2.06 + 0.53 57 1.78 + 0.30 1.83 + 0.31