Risk Factors (1)

Robert W. Griffith, MD
March 24, 2000 (Reviewed: October 9, 2002)

Introduction

As health professionals, we have probably all seen a patient and said to ourselves "there goes an MI waiting to happen". As good health professionals, we tell the patient this, in a suitable way, and give appropriate advice. But how often do we check to see if our advice is being followed? Many patients these days really want to know how to stave off disease as long as possible, and it is the duty of health professionals to provide the necessary knowledge to help them. It's also our duty to give this type of counsel early enough for effective preventive action.

At HealthandAge.com we have considered the changing demand towards prevention, rather than treatment, and we have assembled a number of articles, summaries, and links to other sites grouped under the heading "Risk Factors". These are aimed at both health professionals and the public, according to their specific needs.

Development of the Risk Factor Concept

"But when one particular species of events has always, in all instances, been co-joined with another, we make no longer any scruple of foretelling one upon the appearance of another, and of employing that reasoning which can alone assure us of any matter of fact or existence. We then call one object "cause" and the other "effect". David Hume

Determining the etiology of disease has always been important to physicians. The development of science and skills over the centuries led to the cause of many diseases becoming known by the early 19th century. However, the concept that a "cause" need not always be followed by the expected "effect" was necessary to allow the establishment of risk factors. The science to study these associations was called epidemiology.

In the 1840s Lemuel Shattuck, a Boston physician, introduced the registration of births and deaths, and the cause of deaths. His analyses of the resultant data led to several important improvements in public health. Meanwhile, in London, John Snow demonstrated an association between an outbreak of cholera and the use of a Soho water pump. In this case, drinking water from the pump was clearly a risk factor - not everyone who drank from the pump got cholera, while some who got their water elsewhere did. The bacillus Vibrio cholerae was not discovered for another 30 years, but its detection provided an early example that there are intermediates between risk factors and the conditions associated with them.

There were few major outcomes of epidemiology until the 1950s, when an association between cigarette smoking and lung cancer was established, both in the USA and the UK. A few years later the first big insurance company study was published, showing the risk of premature death associated with high blood pressure.

In 1948, the Framingham Heart Study - under the direction of the National Heart Institute - recruited 5,209 men and women between the ages of 30 and 62 from the town of Framingham, Massachusetts, USA, and undertook extensive physical examinations and lifestyle interviews that were analyzed for common patterns related to cardiovascular disease development.¹ Since 1948, the participants have continued to return to the study every two years for a detailed medical history, physical examination, and laboratory tests, and in 1971, the study enrolled a second-generation group - 5,124 of the original enrollees' adult children and their spouses - to participate in similar examinations. In the past 50 years, the study has produced about 1,000 articles in leading medical journals.

Additional major prospective epidemiological studies of lifestyle and other risk factors were conducted in cohorts of workers, largely in Chicago. The Chicago Peoples Gas Company Study began in 1956, the Western Electric Study in 1957, the Chicago Heart Association Detection Project in Industry in 1967, the US Railroad Study in 1957, and the National Co-operative Pooling Project in 1964. These studies led to numerous publications giving quantified risk factors for overall mortality, cardiovascular mortality, overall cancer mortality, and lung cancer.

The US Department of Veterans Affairs Cooperative Study Group was the first large study to show that the treatment of hypertension lowered the risk of stroke and death from cardiac disease. Finally, the MRFIT study (the Multiple Risk Factor Intervention Trial) reported in 1980 the effects of over 10 years' modification of cardiovascular risk factors in hypertensive patients, demonstrating conclusively the benefits of multifactor intervention.

Fixed Risk Factors

Obviously age, sex, and genetic makeup are risk factors that do not lend themselves to management. However, hormone replacement therapy (HRT) can mitigate the risks of diseases associated with postmenopausal estrogen lack (osteoporosis, cardiovascular disease, possibly Alzheimer disease), so that some risks associated with gender can be influenced to a certain degree. Practical applications of genetic engineering, now on the horizon, may allow some hereditary disorders to be eliminated in "treated" individuals.

Patients should be informed of any condition to which they are more prone due to their age, gender, or family history, so that they can address any changeable risk factors for that disease, to try and compensate for the fixed risk.

Changeable Risk Factors

The usual "target" for risk factor management is coronary artery disease (CAD). It is generally accepted that sufficient exercise, not smoking, and a low-fat diet will go a long way to staving off a myocardial infarction (MI) at an early age. But these lifestyle adjustments have beneficial effects on other conditions. Regular exercise lowers the risk of developing type 2 diabetes and hypertension. Not smoking markedly lowers the risk of for emphysema (chronic obstructive pulmonary disease, COPD), lung cancer (and other cancers), as well as age-related macular degeneration (AMD). In other words, addressing one risk factor can improve the outlook for avoiding or postponing a number of serious conditions, or end results. On the other hand, in order to preclude a particular end result it is often necessary to address several risk factors.

Risk factor modification may be started at various stages. Ideally, if the risk for a disease is recognized before there is any evidence of it or its forerunner, because of the patient's family history, gender, or lifestyle, preventive action should be instituted as early as possible. Commonly, however, the first signs of increased risk are found when the patient has a physical exam or lab tests. These "silent" changes can sometimes be addressed by lifestyle changes, but more often require medication (e.g. antihypertensives, lipid-lowering agents).

Stroke and cancer - by far and away the major killers of older persons - are not readily found on casual, routine lab tests or exams; they have to be sought for. The rewards of early detection, however, are such that greater expenditures of time and money for this are fully justified.

It should be emphasized that there may be synergy between risk factors for a given disease - i.e. if two specified risk factors are present, the actual risk is greater than the two risks added together. Some risk factors are, however, totally independent.

Summary

The existence of risk factors for a large number of diseases has led to a surge of interest in improving lifestyle in order to prevent or postpone ill health. It is envisioned that the future practice of medicine will largely be dedicated to preventing, in addition to treating, diseases. Knowledge of which risk factors are relevant for a particular disease allows the most appropriate steps to be taken. If health professionals do not provide this information, people will get it elsewhere - possibly with less-than-optimal results. Regular physical check-ups, including lab exams, will detect any "silent" risk factors, such as high blood pressure or a high cholesterol level that can be taken care of before they lead to disabling illness. They also provide the physician with an ideal opportunity to emphasize the benefits of a healthy lifestyle, and correct any obvious deviations. By these means, the onset of many diseases may be postponed until late in life. You can explain to your patients that they should live better today, so that they age better tomorrow.

The discussion of Risk Factors is continued in the second article - Risk Factors (2)

Footnotes
1. See http://www.nhlbi.nih.gov/about/framingham/index.html

Please take a moment to give us your comments. For questions about Health matters you may check our "Questions & Answers" Portal and Service.