WHY IT WORKS
Every plant that thrives in the sun, does this because it is able to produce it's own powerful sunscreening compounds.
Because there is an intimate evolutionary relationship between our biology and the consumption of plants our bodies rely on these compounds to be in our diet.
Studies show that carrotenoids - the photoprotective pigments produced by many plants - accumulate in the skin and eyes where they act as sunscreening molecules and antioxidants.
Plants produce photoprotective molecules in response to the UV light they are subjected to.
High UV light, temperature fluctuations, lack of water cause plants to protect themselves by producing high amounts of photoprotective and antioxidant molecules.
Plants that are grown in polytunnels which filter out the UVB light have low levels of these beneficial compounds. And so are our diets and bodies.
Sun induced skin damage isn't caused by the deficiency of synthetic petrochemical filters in the skin, but by the lack of UV protective fatty acids, vitamins, antioxidants and carotenoids in the diet.