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Roughly six in ten American adults are living with at least one chronic disease, and about four in ten have two or more. Globally, the World Health Organization counts around 41 million deaths a year from noncommunicable diseases, close to three-quarters of all deaths. These are not rare conditions or edge cases. They are the everyday backdrop of adult medicine.
The seven below carry most of that weight. They are ordered roughly by how many people they touch and how much damage they do, and each one comes with the risk factors that genuinely matter.
1. Heart Disease
Heart disease has held the top spot in the United States for decades, killing around 695,000 people a year. The most common form is coronary artery disease, where plaque narrows the arteries feeding the heart muscle. It builds quietly for years before the first chest pain appears.
It is not only about heart attacks
Plenty of heart problems have nothing to do with blocked arteries. Aortic stenosis, a narrowing of the valve blood exits the heart through, affects roughly 2% of people over 65 and closer to one in eight past 75. Typical signs are breathlessness on mild exertion, chest tightness, dizziness, or fainting. Because those symptoms creep in gradually, many people write them off as ordinary aging.
The risk factors are familiar: high blood pressure, high LDL cholesterol, smoking, diabetes, a family history of early heart attacks, and a sedentary routine.
2. Type 2 Diabetes
About 38 million Americans have diabetes, and roughly 8.7 million of them do not know it. Another 98 million adults have prediabetes, a blood sugar range that is not diabetes yet but often turns into it.
Diagnosis usually hinges on one number. An A1C below 5.7% is normal, 5.7 to 6.4% is prediabetes, and 6.5% or above is diabetes.
Why the complications matter more than the label
Persistently high glucose damages small blood vessels, which is why diabetes shows up later as nerve pain, kidney damage, vision loss, and slow-healing foot wounds. It also roughly doubles the risk of heart attack and stroke.
There is unusually good evidence that this can be slowed. In the Diabetes Prevention Program, adults at high risk who lost 5 to 7% of their body weight and walked about 150 minutes a week cut their progression to diabetes by 58%.
3. Cancer
Cancer is the second leading cause of death in the US, with close to 2 million new diagnoses a year. Age is the strongest single risk factor. Most cases appear after 50 because genetic damage accumulates with every cell division over a lifetime.
Screening ages have shifted in recent years. Colorectal screening now starts at 45, mammography at 40, and yearly low-dose CT is recommended for adults 50 to 80 who have a 20 pack-year smoking history and currently smoke or quit within the past 15 years.
Timing changes outcomes dramatically. Five-year survival for breast cancer caught at a local stage is around 99%. Once it has spread to distant organs, that figure drops to roughly 31%.
4. COPD and Asthma
Chronic respiratory disease is a broad label covering COPD, asthma, and occupational lung conditions. COPD alone is the fourth leading cause of death worldwide.
COPD
About 16 million US adults have a COPD diagnosis, and researchers estimate millions more have it without knowing. Smoking is the biggest driver, yet roughly one in four people with COPD never smoked. A cough that produces phlegm most mornings, or getting winded on a single flight of stairs, is worth a spirometry test.
Asthma
Asthma affects around 25 million Americans. It gets filed away as a childhood disease, but it can start or return at any age, and adults tend to have more persistent symptoms than children. Knowing which asthma triggers set off your own flare-ups, and the difference between a controller inhaler and a rescue inhaler, is what keeps people out of the emergency room.
5. Arthritis
More than 58 million US adults, about one in four, live with some form of arthritis. Osteoarthritis, the wear-and-tear type, is the most common. Rheumatoid arthritis is different: an autoimmune disease that can attack joints, lungs, and eyes, and needs early treatment to prevent permanent joint damage.
Arthritis is one of the leading causes of work disability in the country. Movement is the most underrated treatment. Walking, cycling, swimming, and light strength training all reduce pain and protect the joint better than rest does. Steroid injections and physical therapy help, though they work best alongside activity rather than instead of it.
6. Chronic Kidney Disease
Around 35.5 million US adults have chronic kidney disease, and most have no idea. There are essentially no early symptoms. Diabetes and high blood pressure cause about two-thirds of cases between them.
Two cheap tests catch it: an eGFR from a standard blood draw and a urine albumin-to-creatinine ratio. An eGFR below 60 for three months confirms CKD; below 15 is kidney failure. The stakes are high because kidneys do not regenerate, and dialysis is a gruelling routine that consumes three days a week.
7. Alzheimer’s Disease and Other Dementias
About 7 million Americans aged 65 and older are living with Alzheimer’s, and the number keeps climbing as the population ages. It is not a normal part of getting older. Forgetting where you left the keys is ordinary. Forgetting what the keys are for is not.
The 2024 Lancet Commission on dementia identified 14 modifiable risk factors, including untreated hearing loss, high LDL cholesterol, social isolation, depression, and physical inactivity. Together they account for an estimated 45% of dementia cases, which is a striking amount of room to work with.
The Chronic Conditions That Slip Under the Radar
Seven entries cannot cover everything. Two conditions that never appear on leading causes of death lists still shape millions of adult lives. Eczema affects more than 16 million US adults and brings relentless itch, cracked skin, and broken sleep. Prostatitis sends a large share of men to a urologist at some point and is a common source of pelvic pain and urinary trouble. Neither is fatal. Both are chronic, and both are routinely underestimated.
What Actually Lowers Your Risk
Genetics load the gun; daily habits largely decide whether it fires. The interventions that move the needle are unglamorous and extremely well documented.
- Know four numbers. Blood pressure (ideally under 130/80), A1C, LDL cholesterol, and waist circumference tell you more about your next 20 years than almost anything else.
- Move more than you think you need to. 150 minutes of moderate activity a week, plus two sessions of strength work, lowers risk across heart disease, diabetes, and dementia.
- Quit smoking at any age. Stop before 40 and you avoid roughly 90% of the excess risk of dying from a smoking-related disease.
- Protect your sleep. Seven to nine hours. Loud snoring and waking unrefreshed can signal sleep apnea, which pushes blood pressure and blood sugar upward.
- Keep your screening appointments. Cancer, kidney disease, and prediabetes are all far easier to manage before they produce a single symptom.
Nothing on that list is dramatic, and that is the point. Chronic disease takes 20 or 30 years to develop, which is exactly why small, repeatable choices have so much room to work with. Pick one item, hold it for a year, and you will have changed the trajectory of at least one of these seven conditions.
