A City Guide To Hegang for and so we address these where possible see also Chapter It is worth remembering that what is considered health-risk behaviour has changed over the past century as medical understanding has developed; for example, we know now that smoking and excessive exposure to the sun carry significant risks for development of some cancers, whereas our ancestors did not. To further muddy the waters, there is also evidence of health benefits of some behaviours considered generally as risky’. Perhaps the best example is sun exposure, receiving growing attention in relation to skin cancer risk, yet in the early twentieth century sun exposure was considered useful in the treatment of skin tuberculosis, and today sunlight therapy may be offered in the treatment of skin disorders. Furthermore there is some tentative evidence relating vitamin D levels which are raised with sunlight exposure to reduced cardiovascular risk Ness et al Later in this chapter we also raise the issue of beneficial effects of moderate alcohol consumption. In order to test the nature and extent of associations between behaviour and health, longitudinal studies are necessary. The Alameda County study is notable in this regard e.g. A City Guide To Hegang 2016.