A clinical trial is taking place at the University of Southampton to see if Vitamin D supplements help the development of babies' bones
So far 500 babies have been born to mothers taking the supplement.
The study examines if a lack of Vitamin D in pregnancy leads to babies developing conditions such as arthritis in later life.
The study is headed by Dr Nicholas Harvey.
He says “We are delighted with the excellent progress of the study and that the 500th baby, Rowen, has been born and is doing well. Recruitment is ongoing in Southampton and the results of this study are likely to have important implications for public health policy- we are really grateful that so many women in Southampton are prepared to give up their time to take part in this important work.”