Babies can't safely get the vitamin D they need from the sun. Your skin is very sensitive and should not be exposed to direct sunlight. Breast milk is the ideal and recommended food for babies, but it's not a good source of vitamin D. Breast milk alone doesn't provide babies with an adequate amount of vitamin D.
Soon after birth, most babies will need an additional source of vitamin D. Although some people choose not to take a supplement during the summer months, when they are exposed to adequate sunlight, people who are at greater risk of vitamin D deficiency, as well as pregnant and breastfeeding women, are advised to take a supplement year-round. While reducing sun exposure is important for preventing cancer, it also decreases the amount of vitamin D a person can produce from sunlight. Breast milk does not naturally contain high levels of vitamin D, since, in the past, babies absorbed most vitamin D when exposed to sunlight.
As a nursing mother, if your own vitamin D levels are low, you may want to consider taking a vitamin D supplement to meet your own needs and increase levels in breast milk. The Department of Health indicates that people may consider taking 10 micrograms (400 IU) of vitamin D a day to keep their bones and muscles healthy. Because vitamin D is essential for promoting calcium absorption in the body, vitamin D deficiency is characterized by conditions such as rickets (in children) and osteomalacia (in adults), and can lead to osteoporosis if left uncontrolled in the long term. Specifically, the PHE suggests that adults and children over one year of age consider taking a daily supplement containing 10 micrograms (400 IU) of vitamin D, especially during the fall and winter, when the sun isn't strong enough.
While there's no risk of your body producing too much vitamin D from sun exposure (although regular precautions should be taken to cover or protect your skin before it turns red or starts to burn), you could consume too much vitamin D through supplements. If you decide to supplement your baby and you don't like taking vitamin supplements other than D (since milk alone provides optimal amounts of those other nutrients), ask your doctor to recommend a preparation that only contains vitamin D to your baby. Knowing that breast milk is specifically designed for your baby and is the most nutritionally and immunologically complete food, it may seem confusing to be told that a breastfed baby needs vitamin D supplements. The guidelines indicate that, while approximately one in five people has low levels of vitamin D, this is not the same as a vitamin D deficiency, and most people are asked to consider taking supplements.
Once a child has started eating solid foods, parents can ensure that their child gets enough vitamin D from food or supplements. However, the desire to avoid overexposure and sunburn has overshadowed the ability of children and adults to absorb adequate amounts of sunlight to maintain normal vitamin D levels. The Department of Health currently recommends that all babies from birth to one year old (including breastfed and formula-fed babies who consume less than 500 ml a day of infant formula, already fortified with vitamin D) and all children aged one to four years old receive a supplement, regardless of whether you are taking a supplement yourself. Breast milk remains the best source of nutrition during the first year, with adequate introduction of complementary foods starting at about six months, which may include foods rich in vitamin D.
