Although the sun's rays help the body to produce Vitamin D which is important for healthy bones and vital bodily functions, the long term damage that can be caused by the sun's rays can outweigh the benefits with up to 16,000 new skin cancer cases being diagnosed each year in the UK alone. There have been lots of studies that prove even using even high levels of sun protection do not cause vitamin D deficiency. Ultrasun is a filter not a sun block, so your skin still functions – i.e. tans, melanin develops, receives vitamin D, but slower. In addition, the British Association of Dermatologists (BAD) state that continued sun exposure does not result in ongoing vitamin D production*, so there's no benefit in sunbathing for long periods of time purely to increase vitamin D levels. If you have any concerns about your vitamin D level you should consult your doctor who can advise you on supplements or diet. *https://www.bad.org.uk/sunscreen-application-does-not-prevent-vitamin-d-production-in-the-majority-of-people/