Vitamin D deficiency is widespread and linked to decreased bone mineral content. Little data exists regarding the vitamin D status and the relationship of 25-hydroxyvitamin D (25-OHD) status to functional bone health outcomes in Hispanic infants. To evaluate this, we plan an observational cohort of full term, healthy, exclusively breastfed Hispanic and Caucasian infants. We hypothesize serum 25-OHD measured in cord blood will be significantly lower in Hispanic than Caucasian infants, with 25-OHD less than 20 ng/mL found in at least 50% of Hispanic neonates. Secondary aims evaluate the relationship between 25-OHD levels and bone mineral status at baseline and after 3 months of 400 IU/day supplemental vitamin D3. Whole body bone density scan (DXA) and bone ultrasound (SOS U/S) will be measured shortly after birth, then again after supplementation. Data from this study will provide information needed to design further randomized trials and interventions.

In recent years, severe vitamin D deficiency has resurfaced as a major public health concern. Nutritional rickets is widespread, and a recent report on this disease in Texas showed Hispanic children are at increased risk. Long-term follow-up has demonstrated that vitamin D deficient infants are more likely to have decreased bone mineral status in late childhood. Additionally, vitamin D deficiency has been linked to changes in fetal "imprinting" and increased susceptibility to autoimmune diseases, immune deficiency, and malignancy. At birth, an infant's vitamin D status is entirely dependent on the vitamin D status of the mother. Many studies have shown vitamin D deficiency is very common in mother-child pairs, especially in dark-skinned individuals. However, few data exist regarding the vitamin D status in Hispanic infants. Low milk intakes and decreased sun exposure with urbanization makes this a very high-risk group among infants in Texas.

Potential subjects will be identified by study personnel in labor and delivery at St. Luke's and Ben Taub Hospitals and in the normal newborn nurseries. The parent/guardian will be approached and the study will be explained in full. A time for questions will be allowed. Once the parent/guardian agrees to his/her child's participation, an informed written consent form will be signed. Subject confidentiality will be maintained within limits of the law. All names and personal information will be accessed only by the investigators and authorized personnel. There will be no possibility of coercion as subjects will not have any relationship of dependency with the investigators.

A cohort of Hispanic and Caucasian infants will be recruited and followed. Other ethnic groups will not be excluded, but will not be analyzed in terms of the primary outcome. Race and ethnicity will be classified according to mother's self classification. The interventions will not differ between the groups.

This study includes 3 study visits:

1. Baseline inpatient visit at birth - while hospitalized to obtain consent, obtain cord blood sample, and mother to complete a questionnaire
2. 1 week after initial hospital discharge - first outpatient visit to obtain other baseline data (see below) and to start the vitamin D drops
3. At 3 mo of life - second outpatient visit to obtain final data (see below) and discontinue vitamin D drops

Visit 1 (Inpatient): After consent has been obtained and upon birth, cord blood will be obtained and analyzed using the Diasorin RIA for 25-OHD. In addition, serum ionized calcium and intact parathyroid hormone (PTH) concentration will be measured on cord blood. Mothers will be given a brief questionnaire to determine their risk of vitamin D deficiency (do they take vitamins, supplements, sun exposure). Follow-up outpatient appointments will be scheduled.

Visit 2 (First Outpatient Visit): Infants will have a speed of sound ultrasound (SOS U/S) and whole body dual-energy x-ray absorptiometry (DXA) performed at 1 week after hospital discharge. Supplements of 400 IU of vitamin D per day will be provided for all infants free of charge starting at the time of the body composition analysis (Vitamin D supplementation is recommended by the American Academy of Pediatrics for all infants who are exclusively breastfeeding).

Visit 3 (Second Outpatient Visit): Infants will return at three months of age and repeat measurements of serum 25-OHD, PTH, bone SOS U/S, and whole body DXA will be performed. At this time a second brief questionnaire will be given to the mother to assess the risks of vitamin D deficiency in the child. Vitamin D drops will be discontinued.

Between visits, investigators will call the family to check on breast feeding status.

At delivery, cord blood will be obtained and analyzed for 25-OHD, serum ionized calcium, and intact parathyroid hormone (PTH) concentration. At three months of age blood will be drawn for 25-OHD and PTH. The purpose of the blood draw is to assess the vitamin D status in the newborn infant. This is the primary aim of the study.

• 5 cc (one teaspoon) of cord blood will be obtained at visit 1, and 5 cc (one teaspoon) blood will be drawn from patient at the third visit (three months of age).
• Total = 2 teaspoons

There will be no study costs passed on the subject's family. Study investigations (laboratory, bone mineral assessment) will be paid for by the researchers. Costs for routine medical care, not associated with the study, but associated with delivery and hospitalization of the newly born child will be the responsibility of the family and their insurance company.

A total of 60 subjects will be enrolled in the protocol. Enrollment of 30 Hispanic infants and 30 Caucasian infants will provide a power > 80% to demonstrate a significantly lower cord 25-OHD concentration in Hispanic infants at p<0.05, the primary outcome.

Inclusion Criteria:

• Full term infants (37-42 weeks)
• Appropriate for gestational age
• Free of major congenital anomalies
• Born to mothers without a history of diabetes or chronic illness who intend to exclusively breastfeed

Exclusion Criteria:

• Any child who does not meet the above inclusion criteria
• Insufficient cord blood available to determine cord 25-hydroxyvitamin D status