Monitoring of 25-OH vitamin D levels in children with cystic fibrosis

Abstract

Background: Patients with cystic fibrosis are at risk for malabsorption of fat-soluble vitamins, and those with low 25-OH vitamin D levels have a higher risk of low bone mineral density and long-term skeletal complications. It is currently recommended that vitamins A and E be monitored yearly; however, no recommendations exist for 25-OH vitamin D. Because all three vitamins are fat-soluble, the hypothesis in the current study was that low levels of vitamins A and E could identify patients at risk for low 25-OH vitamin D, so that 25-OH vitamin D measurements could be obtained in only selected circumstances.

Methods: Forty (21 girls) patients with CF, age 10.5 +/- 3.9 (SD) years, were assessed in a cross-sectional survey for ideal weight for height (percentage of predicted), spirometry (percentage of predicted FEV1, 33/40 patients), and serum levels of vitamins A, E, 25-OH vitamin D, and cholesterol (37/40 patients).

Results: Nine (22.5%) of 40 patients were malnourished (percentage of predicted ideal weight for height <85%), 7 (21.2%) of 33 had moderate to severe lung disease (FEV1 <60%), 4 (10%) of 40 had low levels of vitamin A, 3 (7.5%) of 40 had low vitamin E levels, 4 (10.8%) of 37 low vitamin E/cholesterol levels, and 4 (10%) of 40 had marginal or low levels of 25-OH vitamin D (<40 mmol/l). The patients with low 25-OH vitamin D were older, with no child < 12 years of age having a 25-OH vitamin D level less than 40 mmol/l. They also had lower vitamin E and vitamin E/cholesterol levels than those with normal 25-OH vitamin D levels. The groups did not differ in percentage of predicted ideal weight for height, lung function, or vitamin A levels. The best positive predictor for 25-OH vitamin D less than 40 mmol/l was low vitamin E (66.7%), with a negative predictive value of 94.6%. 25-OH vitamin D levels correlated with vitamin E/cholesterol levels (r = 0.41, P < 0.01) and weakly with vitamin E levels (r = 0.28, P < 0.08), but not with vitamin A levels.

Conclusions: These results suggest that children aged less than 12 years and older children with normal vitamin E levels are especially unlikely to have low 25-OH vitamin D levels, and this measure can therefore be omitted. In contrast, those children with low vitamin E levels may warrant monitoring.