7-Dehydrocholesterol has significant absorption of UV light at the lowest wavelengths of light found in sunlight (290-310 nm). Hence the need for full-spectrum lamps to emit UV-B radiation (UV-B light is defined here to be light between 290-315 NM).
In rare cases some vegans might not get enough fat or calories to produce adequate amounts of steroid hormones (which are produced from cholesterol). Two studies have shown vegans to have sex hormones on par with meat-eaters (1, 2), but one report showed vegan women to have lower levels of estrogen (3).
However, a diet rich in fruit and vegetables that is typical of a vegan diet has a positive effect on the calcium economy and markers of bone metabolism in men and women (49). The high potassium and magnesium content of fruit and vegetables provides an alkaline ash, which inhibits bone resorption (53).