Public health measures are probably responsible for most of the increase in average human life expectancy that occurred during the 20th century. Crusaders for clean water and milk, sanitary sewers, and vaccination drives aimed to control the great killers of humanity, infectious diseases. One measure of success is that in 1900, 80 percent of all deaths were from communicable diseases; today non-communicable diseases account for 80 percent of deaths.

But that success has bred unrealistic expectations. Now many public health officials want to move from keeping infectious diseases in check to controlling lifestyle diseases.

New York City is at the forefront of this new public health movement. In January, city health officials began requiring that medical testing labs report the results of blood sugar tests for all the city's diabetics directly to the health department. This is first time that any government has begun tracking people who have a chronic disease. The New York City Department of Health will analyze the data to identify those patients who are not adequately controlling their diabetes. They will then receive letters or phone calls urging them to be more vigilant about their medications, have more frequent checkups, or change their diet.

For centuries, governments have asserted authority to monitor and even control the actions of people who carry infectious diseases. For example, in the 14th century, Venice invented the practice of quarantine which required that ships from infected plague ports wait at anchor for 40 days (quaranta giorni) before landing. Quarantine laws in the United States was used to isolate Mary Mallon, a.k.a, Typhoid Mary for years and more recently in New York City to detain 200 or so carriers of infectious tuberculosis who were refusing treatment.

The U.S. Centers for Disease Control and Prevention has the authority under the Public Health Service Act to apprehend, detain, or conditionally release individuals in order to prevent the introduction, transmission, or spread of suspected communicable diseases including cholera, diphtheria, infectious tuberculosis, plague, smallpox, yellow Fever, viral hemorrhagic fevers (Lassa, Marburg, Ebola, Crimean-Congo, South American, and others not yet isolated or named) and severe acute respiratory Syndrome (SARS). Owing to concerns about an outbreak of bird flu, President Bush issued an executive order last spring permitting quarantine of people carrying influenza caused by novel or reemergent influenza viruses that are causing, or have the potential to cause, a pandemic.

Similarly public health officials have long required the reporting of sexually transmitted diseases so that past partners could be traced and warned that they might be infected. Even the draconian new anti-smoking laws that are sweeping the country are being justified on the grounds that second-hand smoke harms the health of others.

But this is where the similarities between contagions and lifestyle diseases end. Diabetes is not infectious, nor do diabetics in restaurants endanger the health of other diners.

Make no mistake about it: Diabetes is on the rise in the United States, increasing from 6 million diagnosed with the disease in 1980 to 15 million in 2004. And the medical consequences of uncontrolled diabetes are devastating, including heart disease, strokes, kidney failure, blindness, and progressive limb amputations. The disease shortens a person's life expectancy by as much as a decade.

So what could be wrong with merely monitoring and reminding people to take better care of themselves? New York City Health Commissioner Thomas Friedan has made it clear that it won't necessarily end there. If nagging is not sufficient to reduce the health consequences of the disease, other steps will be taken. Friedan argues that "modifications of the physical environment to promote physical activity, or of the food environment to address obesity, are essential for chronic disease prevention and control." Friedan envisions regulations for chronic disease control including "local requirements on food pricing, advertising, content, and labeling; regulations to facilitate physical activity, including point-of-service reminders at elevators and safe, accessible stairwells; tobacco and alcohol taxation and advertising and sales restrictions; and regulations to ensure a minimal level of clinical preventive services."

At its most draconian, one can imagine that local public health officials might impose a severe tax or even outlaw foods that they believe contribute to the diabetes "epidemic." No more Twinkies or French fries. Buildings would have to be redesigned not only to accommodate the physically handicapped but also in ways that somehow encourage the physically able take the stairs. And do regulations "ensuring clinical preventive services" mean mandatory health checkups? Wouldn't it be more efficient just to tax people for every extra bit of avoirdupois they carry over a body mass index of 25?

Using a public health rationale to control diseases that result from lifestyle choices could easily spread beyond diabetes. After all, the leading causes of death are now non-communicable diseases like heart disease, strokes and cancer. These diseases are affected by many of the same risk factors as diabetes. One can imagine health authorities requiring medical laboratories to report the results of one's cholesterol and blood pressure tests. If your "bad" LDL cholesterol is too high, you could be reminded to take your statin drugs, cut back on the steaks or get to the gym more often.

If the United States finally succumbs to universal government funded health care, health bureaucrats will no doubt justify their intervening in the exercise, dining, transportation, smoking, drinking, and recreational drug choices of Americans on the grounds that they are saving taxpayers money. We might all live longer, but we will certainly be enjoying it less. "There are lots of good reasons to do this kind of thing, but the questions it raises all have to do with the nanny state: Should the government be collecting this kind of information? Should it be intervening like this?" said Lawrence O. Gostin, who directs the Center for Law and the Public's Health at Georgetown and Johns Hopkins universities in the Washington Post last month. "You can imagine it getting to the point where you have a public health worker showing up at your door and asking, 'Did you remember to exercise, eat right and take your medication today?' "

Given the trend toward ever more intrusive government intervention in health care, New York's proposed cure may well turn out to be worse than the disease.