The prevalence of rickets in the world is on the rise not only in developing but also in developed countries. In Korea, breastfeeding has increased. There have been few studies on the possible association of rickets with breastfeeding. The purpose of this study was to identify the development and the clinical presentation of subclinical rickets in breastfed infants.

We investigated patients who were breastfed and had hypovitaminosis D in the blood from May 2006 to April 2007, and who were diagnosed with vitamin D deficient rickets from May 2003 to April 2006. We evaluated the results of blood tests, x-rays and other relevant information in the medical record. A questionnaire that included questions on the diet of patients, the mothers activity during pregnancy and place of residence was administered.

Twelve patients (66%: male, 34%: female) were enrolled in this study. There were eight in the asymptomatic and four in the symptomatic group. The median age for each group was 8 months (range 4-11 month) and 5.5 months (5-8 month). All patients in the symptomatic group were breastfed until diagnosed. In the asymptomatic group, they were breastfed for four to six months, and then weaned with only thin rice soup and vegetables. Nine patients had a vitamin D concentration below 20 ng/mL and three patients had levels between 20 and 29 ng/mL. Alkaline phosphatase (ALP) and parathyroid hormone (PTH) were elevated in both groups. There were statistically significant 25-OHD₃ levels in the blood in both groups ( P =0.008). Ten of the patients (83%) also had iron deficient anemia.

Vitamin D deficiency and subclinical rickets has been identified in Korea. However, the prevalence of this disease has not been determined. The main limitation of this study was the small number of patients and the absence of a control group.