Studies of strategies to reduce greenhouse
Studies of strategies to reduce greenhouse gas emissions and improve health in urban environments have shown the potential to achieve both environmental and health improvements. For example, modelled effects of low emission vehicles and increased walking and cycling in London and Delhi showed major benefits to health outweighing the increased risk of exposure to road injuries. In the case of London, the main benefits were projected from increased active travel, which reduced the risk of diabetes, ischaemic heart disease, stroke, and other health outcomes related to sedentary lifestyle. In cities with high air pollution levels such as Delhi, a substantial proportion of the health benefits are likely to be due to air pollution reduction. If urban populations in England and Wales had similar patterns of walking and cycling to those achieved in Copenhagen, about £17 billion of costs could be averted from the National Health Service over 20 years, increasing further beyond that period.
Assessments of policies to mitigate environmental change should specifically consider the potential unintended adverse consequences (co-harms). Some types of biofuels, such as corn alcohol, compete directly with important food crops. Diesel engines were promoted in some countries because of their reduced greenhouse gas emissions but have higher emissions of fine particulates and nitrogen oxides. Increasing the hedgehog signaling efficiency of houses by use of improved insulation and draught proofing might increase exposure to household air pollution unless accompanied by improved ventilation to prevent the build-up of harmful pollutants.
Future studies of health co-benefits need more consistent methods, counterfactual scenarios, and timescales to compare the relative cost-effectiveness of different strategies. The concept can be extended to policies to reduce other types of environmental change and future research also needs to consider how improved understanding of co-benefits can most effectively help catalyse action by policy makers to support planetary health.
Urbanisation is a planetary scale change process. In the past 200 years, the proportion of the world\'s population living in cities has grown from about 5% to more than 50%. By 2050, about 2·5 billion additional people will need to be housed in cities—more than 1 million people every week—with about 90% of the increase concentrated in Asia and Africa. Urban land cover is expected to increase by more than 1 million km by 2030, nearly tripling the global urban land area circa 2000, threatening biodiversity and affecting ecosystem productivity through loss of habitat, biomass, and carbon storage. Urban ways of living are the keystone of modern human ecology. Having evolved as hunter gatherers living in natural environments with ready access to a healthy diet and plenty of opportunity for physical activity in daily living, most in the world are now living with a mismatch between their evolutionary biology and their environment. Although, on average, the health of urban dwellers is better than rural dwellers, urban health inequities have been well documented.
Nutritionists are classically concerned with the associations between nutrients and diets and nutrition and health outcomes. Understanding these associations is important. Insufficient and poor quality food, especially during pregnancy and in early childhood is a major contributor to the high burden of undernutrition: globally, 159 million children younger than 5 years are stunted (too short for their age), 50 million children globally are wasted (dangerously thin), and more than 3 million children die every year from causes associated with undernutrition. Simultaneously, nutrition-related chronic diseases such as obesity, diabetes, cardiovascular disease, and some forms of cancer are major contributors to the global burden of disease. Ambitious goals have been set by the international community to eliminate malnutrition in all its forms, and 2016 saw the start of a UN Decade of Action on Nutrition designed to reinvigorate national and international efforts for nutrition.