Yes. The amount of vitamin D produced by the body may be insufficient, especially when there is limited exposure to sunlight and routine use of sunscreens. Since dietary vitamin D is found naturally only in a few foods, such as cod liver oil, dietary intake would not be sufficient for most people. However, in the United States, vitamin D is routinely added to milk, fortified cereals, and fruit juices to ensure adequate dietary availability. Fortification of milk and infant formula has been a real success story in the United States, drastically reducing the rate of juvenile rickets and making it a relatively rare occurrence.
Most people with cystic fibrosis have pancreatic insufficiency, increasing their risk of vitamin A deficiency due to difficulty absorbing fat [ 20 , 21 ]. Several cross-sectional studies found that 15%–40% of patients with cystic fibrosis have vitamin A deficiency [ 22 ]. However, improved pancreatic replacement treatments, better nutrition, and caloric supplements have helped most patients with cystic fibrosis become vitamin A sufficient [ 21 ]. Several studies have shown that oral supplementation can correct low serum beta-carotene levels in people with cystic fibrosis, but no controlled studies have examined the effects of vitamin A supplementation on clinical outcomes in patients with cystic fibrosis [ 21-23 ].
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