Abstract
Background: Vitamin A supplementation is being used successfully to treat some forms of cancer and the degenerative eye disease retinitis pigmentosa. The daily biological need for vitamin A is estimated to be 800 retinol equivalents (RE)/d (2667 IU/d) for adult women and 1000 RE/d (3300 IU/d) for adult men; doses ≥7500 RE (≥25000 IU)/d are considered potentially toxic over the long term.
Objective: We assessed the safety in adults of long-term vitamin A supplementation with doses above the daily biological need but <7500 RE (<25000 IU)/d.
Design: Adults aged 18–54 y with retinitis pigmentosa but in generally good health (n = 146) were supplemented with 4500 RE (15000 IU) vitamin A/d for ≤12 y (group A) and compared with a similar group (n = 149) that received 23 RE (75 IU)/d (trace group). Mean total consumption of vitamin A in group A was 5583 RE (18609 IU)/d (range: 4911–7296 RE/d, or 16369–24318 IU/d) and that in the trace group was 1053 RE (3511 IU)/d (range: 401–3192 RE/d, or 1338–10638 IU/d).
Results: Patients in group A showed an 8% increase in mean serum retinol concentration at 5 y and an 18% increase at 12 y (P < 0.001); no retinol value exceeded the upper normal limit (3.49 μmol/L, or 100 μg/dL). Mean serum retinyl esters were elevated ≈1.7-fold at 5 y and remained relatively stable thereafter. No clinical symptoms or signs of liver toxicity attributable to vitamin A excess were detected.
Conclusions: Prolonged daily consumption of <7500 RE (<25000 IU) vitamin A/d can be considered safe in this age group.