The widest determinants of health

While the social and economic wider determinants of health are vitally important, we should remember the overall setting in which they apply.

Human health is dependent on an adequate food supply, clean air, and clean water. These represent the bottom line. The first two are required for cellular respiration— the basic reaction that converts chemical energy into walking, breathing, talking, and blogging— and the third is required as a reactant or solvent for almost all biochemical reactions in the human body.

We need a 4:1 nitrogen/oxygen atmosphere of adequate density to provide the lungs with a sufficient oxygen partial pressure for gas exchange and blood oxygenation; other atmospheric constituents must be kept within safe limits. We need clean drinking water, in which levels of mineral ions do not exceed the concentrating capacity of the kidneys, and toxin and pathogen loads do not exceed the repair, buffering and immune capacities of the human body. Finally, we require sufficient food to meet the demands of bodily growth and repair, and to deliver fuel for respiration.

While the human body has a remarkable capacity to tolerate variations in the supply and composition of these essentials, and human ingenuity can supply them in some extremely hostile environments for limited periods of time— think deep ocean or space— what’s remarkable is how little we need to consider them in everyday life, at least in the developed world. Thanks to advances in agriculture, in particular the post-war Green Revolution, we have an abundance of cheap food. Photosynthesising plants do most of the donkey work of providing us with breathable air, and legislation such as the UK’s 1956 Clean Air Act (which followed London’s Great Smog of 1952) has helped minimise the health impacts of air pollution. Similarly, the Earth’s biogeochemical cycles provide rainwater which is safe to drink, while over the last two hundred years improvements in water and sewage treatment means that, with relatively straightforward technology, we can safely consume water from our rivers, lakes, reservoirs, and more recently, even the sea.

We live largely within the safe operating space provided by the wider global Earth system. In the developed world we can easily afford the necessary tweaks to ensure the supply of these essentials meets our precise requirements. We don’t have to think about them on a day-to-day basis. While most discussions relating to human health, happiness and prosperity take this context for granted, it’s good to note a couple of exceptions:

A health map for the local human habitat, article in The Journal of the Royal Society for the Promotion of Health, 2006.
Planetary Boundaries, a Nature feature, 2009.

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