The major determinants of health on a population basis are driven by political, economic and environmental factors. Last year, early in the SARS epidemic, information given to the public concentrated on the devastating effects of the disease process. We were slow as a profession to focus on the factors influencing the epidemic. It is hard as doctors to accept that whilst hospitals and intensive care beds make a massive difference to the well being of individuals, they have a very small effect in population terms.

Ultimately the factors which make the biggest difference to population health are those which involve political decisions. As a profession we should be in a strong position to influence these decisions. In practice it is rare for a unified response. The effectiveness of the medical lobby is thus diminished. Politics generally follows a reductionist model, short term over long term goals and simple ideas over complex ideas. The repetition of simple messages is a very effective political tool. All too often the messages are over simplifications at best. At worst they may be completely false.

A unified simple health message has great appeal and the potential to enhance population health. "Smoking kills", is an effective example. It is founded on a huge body of academic evidence. It has gradually gained acceptance within the profession and population and effective public health laws are eventually following more than 50 years after the epidemiological studies led by Sir Richard Doll. Unfortunately a simple public health message has the potential to harm population health. The "Fat is bad" message of the 1980s spawned a multi billion dollar dieting industry while the population became more obese. The "MMR causes Autism" message created a debate which rages despite significant evidence against the hypothesis. In this case the over simplification of an extremely complex issue stifled academic debate. Doctors who challenged the currently accepted paradigm were vilified by colleagues. The battle was fought in the media. Simple but conflicting information and advice created anxiety resulting in a significant drop in immunization uptake. We must avoid the over simplification of complex issues and strive to build a clear evidence base in favour of health interventions.

As family doctors what can we do about the issue of pollution? This year has seen a significant deterioration in air quality. There is an increasing body of evidence relating to the health effects of particulate air pollutants.^1,2 The WHO review confirmed that exposure to particulate matter poses a significant risk to population health at levels significantly below that found in Hong Kong. Epidemiological studies have been unable to demonstrate a threshold of particulates below which there is no threat to health. The concept of a safe level is therefore simple but inaccurate. It is a question of relative risk. Likewise, very small particles which reach the alveoli appear to pose a greater risk to health. Whilst this is intuitively logical, it is also backed by a solid evidence base.

Particulate matter is responsible for the visible pollution and is therefore more noticeable. It varies significantly depending upon environmental factors. During the cool, dry season when the winds blow from the North it predominates. In spring and summer when the winds blow from the South and the visibility improves pollution will leave the front pages of our newspapers. Environmental factors influence the concentration of particulate matter. To blame air pollution on the weather is patently ridiculous.

Visible particulates do not represent the whole air pollution story. The long term effects of lower levels of particulates and the invisible gaseous pollutants is more difficult to quantify but an increasing body of evidence suggests risk which is increasing and already significant. This expanding evidence base will give greater weight to the medical arguments for effective political and economic intervention. Health risks related to pollution like epidemics of infectious disease do not respect borders. It is a clear reality that the health of the population of the people of Southern China is closely related regardless of the arbitrary position of a border. As family doctors a significant part of our job is communication. On an individual level our family medicine vocational training focuses on the dynamics of the consultation process. Understanding the physical, psychological and social interactions and helping our patients negotiate the complexities of decision making at an individualized level. We must use those skills of communication to explain risks that may affect future health. Avoiding oversimplified messages but acting as advocates for population health is our challenge.

Increasing pollution represents a significant threat to long term health. It must be addressed at a political level for the long term benefit of all the people of China. It is a complex process which ultimately is influenced by political, economic and environmental factors. It is an issue of health which is our area of expertise. We must work with our medical colleagues in China and attempt to find a unified voice.