This is a protocol for a Cochrane Review (Intervention). The objectives are as follows:

To determine the effect of vitamin D supplementation given to:

• infants compared to placebo or no intervention on vitamin D deficiency, bone density and growth in healthy term breastfed infants;

• lactating mothers compared to placebo or no intervention on vitamin D deficiency, bone density and growth in healthy term breastfed infants;

• infants compared to vitamin D supplementation given to lactating mothers on vitamin D deficiency, bone density and growth in healthy term breastfed infants;

• infants compared periods of infant sun exposure on vitamin D deficiency, bone density and growth in healthy term breastfed infants.

For each of the above comparisons:

• to determine adverse effects from vitamin D supplementation compared to placebo, no intervention or other interventions in healthy term breastfed infants.