What preventive medicine is and why almost nobody practices it

Preventive medicine is the part of medicine that acts before anything hurts: it keeps a disease from starting, detects it while it still causes no symptoms, or stops one already present from progressing. Put that way it sounds reasonable, and yet almost nobody practices it. In Mexico we go to the doctor when something bothers us, the preventive medical check-up gets postponed year after year, and the "check-up package" offered by laboratories and hospitals feels like an expense without a reason. This text explains what prevention actually is, why "nothing hurts" is not an argument, what each measurement detects and how often to do it, and which part of all this a person can do at home and once a year at the laboratory, without turning their life into a clinic.

What preventive medicine is: three levels with examples

The diseases that kill the most today are not infections but chronic diseases: cardiovascular disease, cancer, chronic respiratory disease and diabetes. The World Health Organization (WHO) estimates that noncommunicable diseases caused at least 43 million deaths in 2021, 75 % of deaths not related to the pandemic, and that 18 million of those deaths occurred before age 70; 82 % of premature deaths are concentrated in low- and middle-income countries, where Mexico sits.^[1] Behind them is a short list of factors that can be measured and moved: raised blood pressure (the leading metabolic risk factor according to WHO), overweight, high glucose, abnormal lipids, tobacco, physical inactivity, alcohol and diet.^[1] Prevention works precisely on that list.

Public health divides prevention into three levels. The U.S. Centers for Disease Control and Prevention (CDC) define them like this: primary prevention intervenes "before health effects occur," with vaccinations and changes to risky behaviors such as eating habits or tobacco use; secondary prevention is "screening to identify diseases in the earliest stages, before the onset of signs and symptoms," with examples such as mammography and regular blood pressure testing; tertiary prevention is "managing disease post diagnosis to slow or stop disease progression," with rehabilitation and screening for complications.^[3]

The part almost nobody practices is the second. We do primary prevention halfway (we get vaccinated as children, we try to eat better), tertiary arrives on its own once the diagnosis is there, but measuring something that does not hurt to find something that cannot be felt requires a conscious decision. WHO names detection and screening as key components of the response to chronic diseases, and notes that interventions delivered early reduce the need for more expensive care later.^[1]

Why "nothing hurts" is not an argument

Hypertension is the clearest example. WHO estimates that 1.4 billion adults aged 30 to 79 had hypertension in 2024, that 44 % of them (about 600 million) did not know it and that only 23 % had it under control.^[2] The reason is simple: "most people with hypertension don't feel any symptoms," and "the only way to detect hypertension is to have a health professional measure blood pressure."^[2] There is no internal signal that warns when pressure moves from 130 to 150; the body gets used to it and carries on.

In Mexico the figure is worse. Using Ensanut 2022 data, Campos-Nonato and colleagues estimate that 47.8 % of adults had hypertension by the ACC/AHA criterion (130/80 mmHg or higher) and that 65.5 % of them were unaware of it; with the classic 140/90 mmHg threshold, prevalence was 29.4 % and 43.9 % did not know.^[5] Among those with a prior diagnosis, only 33.7 % had controlled blood pressure.^[5] And prevalence rises with every decade: 25.5 % at ages 20 to 29, 34.9 % at 30 to 39, 47.0 % at 40 to 49, 61.9 % at 50 to 59 and 74.8 % from 60 onward, by the ACC/AHA criterion.^[5] In other words, by age 40 almost half of Mexican adults are already in the high blood pressure zone, and most of them have not found out.

Something similar happens with diabetes. NOM-015 describes the classic symptoms (urinating a lot, intense thirst, intense hunger and weight loss), but those symptoms appear when glucose is already clearly high; the earlier stretch, the abnormal fasting glucose of 100 to 125 mg/dL that the same standard calls prediabetes, cannot be felt.^[8] Ensanut 2022 found that 10.9 % of adults had a prior diagnosis of diabetes and 30.6 % of high cholesterol, figures that only count those who had already been tested.^[6] In high fasting glucose we explain what each range means.

What prevents what: the table

This is the table worth keeping at hand. Each row is a concrete action, what it detects early, how often the guidelines suggest doing it and where the data comes from. The intervals are those of the Mexican standards and of the USPSTF (the U.S. Preventive Services Task Force); your doctor may shorten them if you have risk factors.

Two remarks on the table. First: only two rows require a needle; the rest comes from an upper-arm device, a tape measure and the watch you may already be wearing. Second: no interval is daily except the ones the watch handles on its own. Prevention is not watching yourself; it is having, once or twice a year, a new point to compare with the previous one. Exactly what to include in that yearly point, by age and sex, is in annual preventive check-up.

Why almost nobody practices it

The Ensanut 2022 numbers say it plainly: in the past year only 12.2 % of Mexican adults had been screened for diabetes, 9.1 % for hypertension, 9.0 % for cholesterol or triglycerides and 9.8 % for overweight or obesity.^[6] Nine out of ten adults went through the year without anyone measuring their blood pressure with the intention of looking for something. We all know we "should get checked"; the reasons it does not happen are more concrete.

• The body gives no warning. Secondary prevention looks for what cannot be felt, and what cannot be felt creates no urgency. Hypertension causes "no symptoms" in most people, and the classic symptoms of diabetes appear when glucose is already high.^[2][8] Pain is a great motivator, and prevention works precisely where there is none.
• The system responds to what hurts. A visit for a symptom has a clear script; a visit "to see how I am doing" requires someone to decide what to look at. NOM-030 provides for screening every three years in adults who attend health institutions, but whoever does not attend for another reason never enters that circuit.^[7]
• The result arrives without its predecessor. An isolated glucose or cholesterol value is compared with the lab range and filed away. Without last year's result next to it there is no way to see the direction, and without direction there is no reason to come back. We wrote about this in the reference range is not your personal norm.
• There are too many things to measure. The list of "everything you should check" is paralyzing. That is why shrinking it helps: the American Heart Association sums up cardiovascular health in eight metrics (diet, activity, tobacco, sleep, weight, cholesterol, glucose and blood pressure), and four of them are numbers a person can know and follow.^[9]
• Fear of the result. Many people avoid measuring because they do not want to know. It is understandable and it is the reverse of how things work: WHO reminds us that what is detected early costs less to care for than what is detected late.^[1] If reading a result makes you anxious, the method is in how to read your results without panicking.

How often should I measure blood pressure and glucose if I have no symptoms?

Blood pressure, at least every three years if it has always been normal and you have no risk factors, and twice a year from age 65; fasting glucose, every three years from age 20 if there is obesity and risk factors, or from 45 if there are none. Those are the minimum intervals of NOM-030 and NOM-015 for screening adults with no known disease.^[7][8] The USPSTF, for its part, recommends screening blood pressure in all adults from age 18 and glucose in adults aged 35 to 70 with overweight or obesity, without setting a single interval.^[4]

Two nuances change the practice. First: a single reading decides nothing. NOM-030 records at screening the average of at least two measurements two minutes apart, and confirms hypertension with the average of at least three measurements taken two weeks later; WHO speaks of readings of 140/90 or higher measured on two different days.^[7][2] That is why home measurement, repeated for a week under identical conditions, is worth more than the stray pharmacy reading. Second: a fasting glucose of 126 mg/dL or more is also confirmed by repeating the test on another day, and abnormal fasting glucose of 100 to 125 is a prompt to repeat sooner, not a verdict.^[8]

If you have risk factors, the calendar gets shorter

NOM-015 lists the factors that bring diabetes screening forward: overweight and obesity, sedentary lifestyle, first-degree relatives with diabetes, age over 45, and in women having had babies over 4 kg or gestational diabetes.^[8] NOM-030 adds, for blood pressure, weight, salt (no more than 6 g a day), alcohol, tobacco and lack of physical activity, and asks for 30 minutes of activity most days.^[7] If you recognize yourself in two or more of these points, "every three years" becomes "every year," and the concrete decision is made by your doctor with your data in front of them.

What you can do: at home and once a year at the laboratory

The prevention that works is the one that fits into a normal life. This is a minimal version, designed for a person with no known disease who wants to stop relying on "nothing hurts."

1. One week of home blood pressure, every three or four months. Upper-arm device, seated, five minutes of rest, two readings two minutes apart, morning and evening; keep the week's average, not the stray readings.^[7] If the average lands at 130 to 139 / 85 to 89, it is not hypertension, but it is a number to bring to the doctor.^[7]
2. Weight and waist once a month. Same scale, same time, fasting. A waist over 80 cm in women or 90 cm in men is one of the risk criteria in NOM-015, and a growing waist is the earliest and cheapest signal there is.^[8]
3. Fasting glucose and a lipid panel at the laboratory. Every three years at minimum, every year if you have risk factors; always after 8 to 12 hours of fasting and, if possible, at the same laboratory so you can compare.^[8]
4. Let the watch do the work. Steps, resting heart rate and hours of sleep record themselves. There is no need to look at them daily: a weekly review of the trend is enough, and that is what a weekly health summary is for. The AHA puts sleep at 7 to 9 hours and activity at 150 moderate minutes a week.^[9]
5. One check-up visit a year, with data. Bring your blood pressure average, your weight and waist, your previous results and the list of screenings that apply to your age and sex.^[4] The visit changes completely when the doctor sees a trend instead of a point.
6. Vaccines and screenings on schedule. Ask at that visit which vaccines are due and book the pending screening: Pap or HPV test, mammogram, colon test, bone density, as applicable.^[4]

None of this requires knowing medicine. It requires keeping each number with its date and having the previous one at hand when the new one arrives. That habit, not the number of tests, is the difference between having data and having prevention.

Warning signs

There are situations in which the question is no longer prevention but immediate care; it is worth having them clear before they occur.

• Blood pressure of 180/120 or higher with symptoms. WHO describes that with very high blood pressure (usually 180/120 or higher) severe headache, chest pain, dizziness, difficulty breathing, nausea, vomiting, blurred vision, confusion or abnormal heart rhythm can appear.^[2] With a reading like that and any of those symptoms, do not repeat the measurement: call emergency services.
• Signs of a stroke. Sudden weakness or numbness of the face, an arm or a leg, especially on one side of the body; sudden confusion or trouble speaking or understanding; sudden trouble seeing or walking; sudden severe headache with no known cause. The CDC say to call emergency services right away with any of them.^[10]
• Chest pain or pressure with shortness of breath. It is on the WHO list of symptoms of very high blood pressure and is not something to save for the check-up: it is an emergency call.^[2]
• High glucose with symptoms. Intense thirst, urinating a lot, intense hunger and unexplained weight loss are the classic symptoms of diabetes according to NOM-015; a casual glucose of 200 mg/dL or more together with them meets the criterion for diabetes.^[8] It is not an emergency on its own, but it is a visit in the coming days, not at the next check-up.

What to bring to the doctor

If you arrive with the context already in order, the visit goes to deciding rather than reconstructing.

1. Your home blood pressure average for the last week, with the device you used and the time of the readings.^[7]
2. Current weight and waist and, if you have them, those from six or twelve months ago.^[8]
3. Your latest laboratory results, with date and laboratory, and the earlier ones if they exist: the direction says more than the value.
4. Family history of diabetes, hypertension, heart attack, stroke or cancer before age 50, because it moves the screening calendar.^[8]
5. The date of your last screening of each kind (Pap or HPV, mammogram, colon, bone density) and of your last vaccines.^[4]
6. Habits in one line: whether you smoke or smoked and for how many years, alcohol, weekly activity and the hours of sleep your watch records.^[9]
7. Three questions: what is due this year for my age and sex, how often to repeat blood pressure and glucose given my risk, and which of all these numbers I should watch most.