Current public health policy is that practically everyone in the UK, including infants who breastfeed exclusively, should have some vitamin D supplementation. The exception is for children having more than 500ml of infant formula daily, because formula is already fortified.¹⁷

Infants need vitamin D along with calcium and phosphorous for healthy skeletal development. Without vitamin D, bone formation (especially of the long bones) may not happen or could be delayed, causing rickets. The build-up of unmineralised bone matrix (osteoid) elsewhere can result in osteomalacia (soft bones) with severe pain and muscle weakness.^18,19

Revised public health guidelines on vitamin D and health were published in July 2016 by the Scientific Advisory Committee on Nutrition (SACN), following an extensive review of the evidence since the last major guidelines on vitamin D were published in 1991. While there was sufficient evidence to recommend a reference nutrient intake (RNI) of 10 micrograms of vitamin D for anyone aged four years and above, the evidence for younger children was less clear cut.¹⁸

Rather than propose an RNI, the SACN’s recommendations for young children is now:

• A ‘safe intake’ of 8.5-10 micrograms (340-400 IU) per day for all infants (including exclusively breast-fed and partially breast-fed infants) from birth to one year of age 
• A ‘safe intake’ of 10 micrograms (400 IU) per day for children aged one to four years.

“The recommendation for exclusively breastfed infants is a change from previous advice,” says SACN. It did not take into account exposure to sunlight, due to the range and complexity of factors that can affect dermal synthesis of vitamin D. However, it said that the RNI and safe intakes refer to intake from all dietary sources: natural food sources; fortified foods (including infant formula milk), and supplements.