I just watched the Netflix series Blue Zones that examined habits of societies of people who were most likely to live more than a century. While I agree with most of the conclusions, there is much left out. The problem with such observational studies is that they are subject to population shift bias, observer bias, and selection bias. Over the last 40 years, I’ve seen hundreds of people die. It is inevitable if you are a critical care physician and even more inevitable if you are also a pulmonary physician specializing in idiopathic pulmonary fibrosis, a terminal disease. So, I have my own thoughts on what it takes to live to be a hundred years old (and what it takes to not die in our ICU). But first, let’s take a look at the three forms of bias.
Population shift bias. On the surface, it would seem to be easy to estimate the life expectancy of a group of people. Just look at all of the death certificates and calculate the average age of death. However, human populations are dynamic, with people constantly moving in and out of a given area. Let’s use an example of a hypothetical group of people living on an island in the Mediterranean. You go to the public records department and pull all of the death certificates for the past 10 years and find that the average age of death is 88 years old. You might then assume that the life expectancy is 88 years. But what if there had been no good-paying jobs on that island for the past 10 years and most of the people under age 65 moved to the mainland to find work? In that case, people born on the island who died before age 65 died somewhere else and this makes the average age of people dying on the island look falsely high. Also, the percentage of people living on the island who are older than 100 (per capita rate of centenarians) will be falsely high.
Population shift bias can also occur if there is a change in the birth rate. Let’s say you are measuring longevity by the average age of people on the same island. Three generations ago, families had an average of 6 children but now, families only have an average of 2 children. As a result, the average age of people on the island at any given time is now higher because there are fewer children. But that doesn’t mean that people are really living long.
Observer bias is a problem with any observational study. Let’s say you find that Seventh Day Adventists have a high percentage of people who live past 100. So, you look at the habits of those people to try to determine why they lived as long as they do. There may be hundreds of variables that make them different than everyone else in the world but if you are trying to prove that it is because of diet, then you will have blinders on and only focus on the observation that Seventh Day Adventists eat a plant-based diet. So, you might conclude that the vegetarianism caused then to live so long while overlooking the fact that Seventh Day Adventists also don’t smoke cigarettes.
Selection bias occurs when you look at a small group of people who have a particularly good or bad outcome and then assume that the group of people is representative of the population as a whole. An example of a selection bias error that is frequently made is nursing homes. It is often said that as soon as a person enters a nursing home, it cuts 3 years off of their life. One might then assume that being admitted to a nursing home causes a shortened life expectancy. However, a 70-year-old who need nursing home care is by definition sick and debilitated. A healthy and active 70-year-old would not be admitted to a nursing home. Entering a nursing home doesn’t make you live shorter, being chronically ill and debilitated makes you live shorter. The same can be said of doctor visits – people who visit doctors ten times a year are more likely to die than people who only visit a doctor once a year. If you fall into the trap of selection bias, then you would assume that seeing a doctor causes you to have a shortened life expectancy whereas the truth is that people who see a doctor more frequently have more serious and complicated diseases than those who see a doctor rarely.
The scientist in me would say that the only sure way to know if a habit will make you live longer is to do a randomized controlled trial, preferably placebo-controlled. But this type of study is impossible when looking at people’s life-long habits. So, everything we hear about the habits of people who live beyond 100 years is affected by these forms of bias. And I freely admit that these biases affect my own thoughts on living to be 100. You’ll see that my list is a lot different than the Blue Zone’s list. But I think you’ll find that my list will give you a better chance of becoming a centenarian. So, here goes:
- Be a non-smoker. It is almost unbelievable that it was less than 50 years since the U.S. Surgeon General first reported that smoking was bad for your health. A study in the New England Journal of Medicine in 2013 found that women who smoke a pack of cigarettes a day live 11 years less than women who do not smoke. For men, smoking reduces life expectancy by 12 years. If you do the math, that works out to 14 minutes of life lost on average for every cigarette smoked.
- Get rid of your gun. Most of the people who die of firearm injuries did so from their own gun or the gun belonging to someone else in the family. The CDC reports that in 2022, 48,117 Americans died from a gunshot – 58% of those were suicides. In other words, a good guy with a gun is more likely to kill himself than to kill a bad guy with a gun.
- Wear a seatbelt. In America, we kill almost as many people with cars as we do with guns. The National Highway Traffic Safety Administration reports that in 2022, 42,795 Americans died in a motor vehicle accident. More than half of the drivers and passengers who died in a car accident were not wearing a seatbelt. In 1984, New York became the first state to legally require people to wear seatbelts – the law was met with outrage by anti-belters who said that it was an encroachment on their personal freedom. Unfortunately, that argument does not fly with widows and orphans.
- Maintain a normal BMI. We define obesity as a body mass index (BMI) greater than 30. Overweight is a BMI between 25 – 30. The National Health and Nutrition Examination Survey (NHANES) found that the prevalence of obesity in the U.S. is now 42%. As Americans have become more obese, a cultural taboo on criticizing obesity has emerged with the result that those who say anything bad about obesity can be accused of “fat-shaming”. But the reality is that obesity is not healthy. It increases the risk for hypertension, diabetes, and sleep apnea all of which can shorten life expectancy. It can cause arthritis that reduces physical activity and increases the risk of falls. A 2014 study found that people with a BMI > 40 have a life expectancy 14 years less than those who with a normal BMI between 18.5 and 25. A 2019 study found that even those with a BMI between 30 – 40 had a reduced life expectancy of 5.5 to 7.5 years compared to normal weight individuals.
- Don’t use drugs. In 2022, 105,452 Americans died from a drug overdose. That’s one out of every 3,000 people and more than died by both guns and motor vehicle accidents combined. The drug that causes the most overdose deaths is fentanyl. Most drug users do not call their local drug dealer asking for fentanyl. Instead, it is mixed with other drugs to potentiate their effects at a low cost. However, street drugs are not mixed by compound pharmacies and instead are mixed in unpredictable amounts by dealers with the result that a drug user does not really know what he or she is getting in a dose from one day to the next. Consequently, dying from a drug overdose is now easier than ever before.
- Get vaccinated. In 2019, 2,854,838 Americans died; of those, 49,783 (2%) died of influenza and pneumonia. In 2021, 3,464,231 Americans died; of those, 416,893 (12%) died of COVID. Last week, for my 65th birthday, I got a flu shot and a pneumonia shot. When they become available later this month, I’ll get this season’s COVID booster. These are some of the best investments you can make in your health. Infections cause inflammation and prolonged inflammation is harmful to the body. Vaccinations also cause inflammation (its how they work) but in contrast, vaccination inflammation is mild and brief – vaccinations stimulate rather than stress the immune system. If you live on a remote island with few visitors, it is easy to avoid respiratory infections since those infections have to be brought to the island by someone who is already infected. But for the rest of us, exposure to infections that have the potential to kill us is unavoidable so our best defense is vaccination.
- Choose your parents carefully. Okay, I know that no one can choose their parents but it is true that the genes that we inherit from them have a big impact on our life expectancy. Evolution has genetically engineered us to be able to live long enough to have children and then raise them until they can be self-sufficient. The current average age of menopause is 51 but in ancient times, it was much earlier, around age 40. Allowing for 15-20 years to fully raise and protect a child, our genes needed to ideally get us to about age 55 or 60. There was no natural selection advantage to having genes that let a person live older than that because those genes did not give a greater survival advantage to one’s offspring. Genes that resulted in high cholesterol or breast cancer didn’t really matter 200,000 years ago because people did not live long enough to get the diseases they cause. Consequently, many families carry genes that that result in fatal diseases that occur in the family members’ 60’s or 70’s.
- Exercise your body. Many studies have shown that people who exercise regularly live longer. There are a lot of reasons for this: lower risk of obesity; lower risk of dying of cardiovascular disease; lower risk of osteoporosis; and better strength and balance that can reduce the chance of falling. However, the most effective physical exercise is a life-long exercise lifestyle rather than a New Years resolution gym membership. Walking can be great exercise but we have unfortunately engineered our communities to encourage sitting in a car rather than walking to workplaces, stores, restaurants, and places of worship. Rather than retiring and moving to a gated community on the outskirts of town, consider moving to a walkable neighborhood – preferably one with a lot of hills.
- Exercise your mind. What allowed humans to become the apex predators on Earth? Some people would say it is the capacity of speech. Others would say the ability to make tools. Yet others would say the dexterity that resulted from opposable thumbs. The reality is that it is verbal communication, tool-making, and complex dexterity were all facilitated by the homo sapiens brain. Every successive branch of hominid evolution has been associated with a larger and larger brain, from homo habilis (640 cc) to homo erectus (1,029 cc) to homo sapiens (1,350 cc). Our brains are like any other organ in our body – they work best when we use them regularly. Ideally, we should be exercising all areas of our brains. Exercise the brain’s motor centers by activities requiring balance and dexterity, for example, tennis or dancing. Exercise the brain’s left cortical areas with reading, creative writing, and conversation. Exercise the brain’s right cortical areas with music and art.
- Be engaged with other people. About 400,000 years ago, human ancestors firs started using spears. Ever since then, humans who lived in communities had an enormous advantage over those who lived solitary lives. The more organized the community, the better it’s chance of survival. Communities have propelled humans to the top of the food chain. We need communities as much as communities need us. Social isolation is associated with a higher risk of depression, suicide, dementia, and early death. Keeping connected with other people helps keep us connected with life. There are endless ways to do it: volunteer, be active in your place of worship, speak with family and friends regularly, even use Facebook.
- Avoid excessive calorie-dense foods. Everyone has an opinion about the best diet for longevity. Vegetarian, vegan, low-carb, herbal supplemented, more olive oil, less nitrates – the list is endless. The reality is that humans are built to be omnivorous and consequently, there are a lot of ways to have a healthy diet, as long as they are nutritionally balanced. The antithesis of nutritionally balanced diets are those that are dominated by calorically dense foods. These include excessively sweetened foods, fast foods, and high fat “junk” foods. MacDonalds french fries, like heroin and Fox News, have been specifically engineered to be addictive after just one bite and make you want more. Daily calorie needs are determined by age and physical activity but 2,000 for women and 2,500 for men is a good average. Why waste so much of that on a Wendy’s Frosty (393 calories), Burger King large fries (448 calories), and a Chic-fil-A wrap (660 calories)? The advantage of diets that are high in vegetables, beans, and whole grains is that you can eat a lot, feel full, and have balanced nutrition – all without breaking the calorie bank.
- Drink in moderation (or not at all). For some people, there is no “safe” amount of alcohol – they are wired for addiction. But one or two glasses of wine a day is OK for most people and may or may not actually be beneficial. However, drinking excessively can unquestionably kill you. Excessive alcohol is involved in one-third of gun-related homicides, one-half of gun-related suicides, and one-third of motor vehicle deaths. In addition, chronic excessive alcohol use can cause cirrhosis, pneumonia, various cancers, and dementia. Overall, alcohol is responsible for 140,000 deaths per year in the U.S.
- Avoid poverty. You don’t need to be extremely rich to live a long life but it is really hard to live a long life if you are extremely poor. Poverty is associated with higher rates of smoking, obesity, drug use, and higher death rates for all of the 14 leading causes of death. Poverty results in inability to afford healthcare, living in crowded and unhealthy conditions, and over-reliance on calorically dense foods. Owning a Tesla won’t make you live longer but having to do all your grocery shopping at the Dollar General and being unable to afford a pneumonia vaccine can make you live shorter. Also, it is a lot more expensive to live to age 100 than to live to age 70, simply because you have to pay for more years of living expenses. So, even a middle-income working couple needs to make careful financial planning to avoid poverty in retirement.
- See your doctor regularly. A good primary care provider is worth his/her weight in gold when it comes to staying healthy and living longer. Even if you walk 5 miles a day, eat a nutritionally balanced diet, and never smoke, there are still things that can happen that are outside of your control. We can’t always prevent high blood pressure, colon cancer, or high cholesterol, no matter how good our lifestyle is. Five hundred years ago, people rarely died of heart attacks, colon cancer, and dementia for the simple reason that they didn’t live long enough to get them. But these are conditions that early diagnosis by your PCP can result in effective treatment. See your doctor once a year for a routine visit and follow all of the recommendations for health screening and preventive care.
Blue Zones is worth a watch on Netflix. But its conclusions are susceptible to being affected by population shift bias, observer bias, and selection bias. My own personal conclusions about longevity are also affected by these same biases. So, take my recommendations with a grain of salt – just don’t overdue it with too much sodium.
September 8, 2023
