Other cases have been reported among the children of some ethnic groups in which mothers avoid exposure to the sun for religious or cultural reasons, leading to a maternal shortage of vitamin D, and people with darker skin need more sunlight to maintain vitamin D levels. Rickets had historically been a problem in London, especially during the Industrial Revolution. Persistent thick fog and heavy industrial smog permeating the city blocked out significant amounts of sunlight to such an extent that up to 80 percent of children at one time had varying degrees of rickets in one form or the other. It is sometimes known "the English Disease" in some foreign languages (e.g. German: Die englische Krankheit, Dutch: Engelse ziekte, Hungarian: angolkór). Skin color theory
Rickets is often a result of vitamin D3 deficiency. The correlation between human skin color and latitude is thought to be the result of positive selection to varying levels of solar ultraviolet radiation. Northern latitudes have selection for lighter skin that allows UV rays to produce vitamin D from 7-dehydrocholesterol.
Conversely, latitudes near the equator have selection for darker skin that can block the majority of UV radiation to protect from toxic levels of vitamin D, as well as skin cancer.An anecdote often cited to support this hypothesis is that Arctic populations whose skin is relatively darker for their latitude, such as the Inuit, have a diet that is historically rich in vitamin D. Since these people acquire vitamin D through their diet, there is not a positive selective force to synthesize vitamin D from sunlight.Environment mismatch: vitamin D deficiency arises from a mismatch between an individuals previous and current environment. This risk of mismatch increases with advances in transportation methods and increases in urban population size at high latitudes.Similar to the environmental mismatch when dark-skinned people live at high latitudes, Rickets can also occur in religious communities that require long garments with hoods and veils. These hoods and veils act as sunlight barriers that prevent individuals from synthesizing vitamin D naturally from the sun.In a study by Mithal et al., vitamin D insufficiency of various countries was measured by lower 25-hydroxyvitamin D. 25(OH) D is an indicator of vitamin D insufficiency that can be easily measured. These percentages should be regarded as relative vitamin D levels, and not as predicting evidence for development of rickets. Asian immigrants living in Europe have an increased risk for vitamin D deficiency. Vitamin D insufficiency was found in 40% of non-Western immigrants in the Netherlands, and in more than 80% of Turkish and Moroccan immigrants.