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Exclusively inhabiting tropical countries such as Sierra Leone, wild chimpanzees lack adaptations to seasonal variations in ultraviolet B (UVB) irradiance from sunlight; since UVB exposure enables vertebrates to synthesize vitamin D, this raises questions about how chimpanzees in mid-latitude zoos are affected by the lower and more variable UVB irradiance in those locations. In a study of zoo chimpanzees in Sweden and other mid-latitude countries, Sophie Moittié and colleagues found not only that chimpanzees' vitamin D levels correlate with UVB irradiance but also that vitamin D levels show no evidence of plateauing as UVB irradiance reaches its highest local levels, suggesting that

averaged across seasons, vitamin D levels in zoo chimpanzees in mid-latitude countries such as Sweden tend to be comparable to those in wild chimpanzees in tropical countries such as Sierra Leone.

adaptations to seasonal variations in UVB irradiance may be emerging in zoo chimpanzees in Sweden and other mid-latitude countries.

providing supplemental vitamin D to chimpanzees in zoos in Sweden and other mid-latitude countries would likely not be beneficial.

zoo chimpanzees in Sweden and other mid-latitude countries tend to synthesize less vitamin D than they are inherently capable of synthesizing.