Scientists have pinpointed the most important decade for your health.

Smoking, drinking, and being inactive become entrenched in the decade between 36 and 46 and are harder to reverse, according to a new study. 

Each year a person continues an unhealthy habit, the damage is compounded, the researchers said.

These habits gradually erode a person’s metabolic and psychological health until they become part of a person’s biology after 46. 

The study out of Finland showed that when a person reaches 30, each additional decade of risky behavior worsened their health through age 50 and beyond.

‘Even a single risky behaviour increases the risk of premature death and diseases, but together with other health behaviours, the impact is cumulative,’ the researchers concluded.

‘Furthermore, the impact of these behaviours on health accumulates throughout a lifetime.’

People who smoked, drank, and were physically inactive through their 20s saw few negative effects then, but those behaviors caught up with them, causing worse mental health, poorer self-rated health, and doubled metabolic risks such as high blood pressure, obesity, or diabetes by age their late-30s. 

People who start engaging in risky behaviors young, such as smoking, are more likely to experience depression and poorer physical health by middle and older age

Finnish researchers gathered patient data from a study spanning 1968 to 2021 on 369 people.

Scientists calculated people’s current risk scores based on how many risky behaviors they maintain currently, from zero behaviors (no risk) to three (the highest risk, i.e., smoking, drinking, and being physically inactive).

A 36-year-old who smokes and drinks but also exercises would receive a two, while a 50-year-old who quit smoking but still drinks and doesn’t exercise would get a score of one.

They also looked beyond what behaviors a person has now. They looked at how many years a person maintained those harmful habits, known as the temporal risk score.

People were told to count how many times they did each behavior at each age checkpoint – 27, 36, 42, 50, 61. Someone who smoked at 27, 36, and 42 but quit at 50, therefore, earned a temporal smoking score of three out of five.

They concluded that people who currently have those risky behaviors had more depressive symptoms based on a scored 16-item questionnaire, higher metabolic risks measured by markers like high blood pressure, large waist, and low ‘good’ HDL cholesterol, lower psychological well-being based on a scored 18-question test, and worse self-rated health.

People who had those behaviors now, as well as in decades previously, were even worse off. 

People who started smoking in their 20s and early 30s, as opposed to those who started in their 40s, were more than twice as likely to exhibit depression symptoms and psychological well-being scores that were 2.3 times worse.

Similarly, people with metabolic risk factors such as high blood pressure early in life were twice as likely to experience chronic metabolic disorders compared to those who began experiencing those risk factors in middle age

Similarly, people with metabolic risk factors early in life were twice as likely to experience chronic metabolic disorders compared to those who began experiencing those risk factors in middle age.

Self-rated health among those with worse physical health early in life saw double the decline in self-rated health versus those who became more inactive in their 40s.

Researchers said: ‘Interestingly, the temporal accumulation of risky health behaviours was particularly associated with depressive symptoms in the present study.

‘These results suggest that the accumulation of risky health behaviours over time may also be one of the important factors when preventing depressive symptoms and depression.’

The study, published in the journal Annals of Medicine had several notable limitations, though. They could not establish that risky behaviors caused poor health, only that they are linked.

Researchers also looked at a few risky behaviors while not considering several others, such as diet, sleep, or drug use.

They also noted that the subjects were Finnish adults born in 1959, a population that may not reflect the United States.

People may have also reported their health and habits through a rosier lens, concealing heavy drinking, misremembering bad habits, or not opening up about depressive symptoms, risking bias.

They concluded that people who currently have those risky behaviors had more depressive symptoms based on a scored 16-item questionnaire in their 40s to 60s

Still, the study’s 30-year longitudinal design and inclusion of several health outcomes, both physical and mental, provide rare and valuable insights into the effects of lifelong habits and whether humans can undo some of the damage.

Smoking is tied to a laundry list of health problems, ranging from myriad cancers to chronic lung and breathing problems.

Drinking excessively is known to cause severe liver damage that can prove life-threatening. And obesity is a leading risk factor for a range of chronic diseases.

Health habits don’t change much during middle adulthood, researchers said, becoming chronic concerns. Their findings stressed the importance of ‘tackling risky health behaviours as early as possible’ to keep these risks from piling up over the years, ‘which can otherwise lead to poor mental well-being and health later in life.’

The US is steeped in an epidemic of chronic diseases, such as cancers, diabetes, heart disease, and high blood pressure.

An estimated 133 million Americans – approximately 40 percent of the US population – have at least one chronic illness. Obesity is the most common among them. Forty-two percent of Americans have it.

Scientists have known for years that lifestyle choices and trauma early in life, particularly childhood, significantly impact one’s health later in life.

But the latest study breaks new ground by revealing that it’s not just what you do, it’s when and for how long you do it.