Synthesis of vitamin D in the skin through the action of sunlight is a major source of vitamin D in parts of the world where foods are not fortified with the vitamin. Skin pigmentation (color), dress habits and season are some of the factors that limit sun exposure and affect vitamin D synthesis in the skin. Maternal vitamin D status is especially important to meet infant needs when newborns are not supplemented with vitamin D. In Ethiopia, vitamin D status of lactating women and infants and breast milk vitamin D concentration have never been assessed. The purpose of this study is to assess changes in maternal and infant markers of vitamin D status before and after vitamin D supplementation of the lactating mothers.

Vitamin D is a vitamin that regulates calcium and phosphorous homeostasis and ensures proper mineralization of bone. Lactating women and infants are considered to be at risk of vitamin D deficiency due to increased needs for vitamin D and calcium. Stores of vitamin D acquired in utero and breast milk are the main sources of vitamin D for infants. Maternal vitamin D deficiency, exclusive breastfeeding, skin pigmentation and limited sun exposure are commonly seen in infants with rickets. However, the UV exposure, dress habits, traditional practices and other risk factors to vitamin D deficiency in Ethiopia have not been explored. This study aims to fill this research gap.

Inclusion Criteria:

• Breastfeeding
• Available for enrollment within 2 weeks of delivery
• Residing in the study area in Ethiopia
• Apparently healthy

Exclusion Criteria:

• Self-reported chronic or acute disease condition
• Not breastfeeding
• Twin births