Normal weight and enough sleep.

Don't compromise it chronically. Protected sex etc.

Sleep, exercise, a balanced diet of mostly whole fruits and vegetables, and a moderate amount of whole grains, legumes and fresh meat/fish/eggs if you're not choosing a vegan lifestyle. Avoid ultra processed foods, cured meats, alcohol and other recreational drugs. Make sure you get enough vitamin D, which can be hard with certain diets if you're not supplementing, or getting the right amount of sunlight(latitude and time of year matters).

Try to stay low stress, spend time out in nature, maintain good relationships, etc.

Edit: caveat to spending time out in nature: be vigilant of ticks. A tick-bourne disease can mess up your immune system pretty well

Maybe your schema will work for someone who’s on the very top point of the bell curve of human population but human genetic and environmental variability will over rule your advice for the majority of people.

The states known for “hippie”/“granola” attitudes, which largely align with the advice given here, tend to live longer than the states that don’t (scroll through the list in [1] to see this). Usually I would insist on a study, but the effect is so striking, and the mechanism by which it would work is so obvious, that I think this simple list is enough. And I’m sure there are studies too, I’m just too lazy to find and link one.

[1] https://en.wikipedia.org/wiki/List_of_U.S._states_and_territ...

Plus, fix your gut.

Don't be a germaphobe. Don't wash your hands a lot. Give your immune system a little work out each day by not babying it.

Try not to take any medicines unless you absolutely need them, and stay away from hand sanitizers. If you do need to clean anything, soap is more than enough and water is usually enough.

I thought it was normal to be over 50 and not take any medicines, but all the doctors and staff were surprised by this when I got my colonoscopy recently.

By hand sanitizers, do you mean something other than the isopropyl-gel based hand sanitizers? If not, I would have guessed that would be little different than using a strong soap.

That said, unfortunately there's some element of luck to it. There's compelling evidence that C-section babies have abnormal immune responses and less diverse body flora. And I imagine childhood circumstance affects things too, city vs country affecting the childhood exposure to pathogens and non-pathogens for training.

Above 50? My 30+ year old American friends are all running on pills, daily, many different of them. I was shocked.

So I am rather with you. It should be normal not to take medicines.

What sort of pills? Vitamins or ?

Some yes, and then all sorts of mood boosters, painkillers, etc. Basically all the stuff I later saw during a commercial break at a bar during some sports game. (this should be banned, TBH)

- Get vaccinated fully and regularly. Any kind of infection is much harder to deal with for the body than a vaccine. Particularly important are the measles and Covid shots, an infection with either of the actual pathogens can wipe out your immune system history and you lose a lot of protection.

- practice safe sex, get tested regularly (even if both you and your partners are exclusive) and get that HPV shot. Yes, even if you're male. Cancer on your bits ain't pretty.

- keep the drug consumption reasonable, especially smoking and alcohol

- the better quality the food, the better your health. Should be a no-brainer and I know about food deserts, lack of time etc

You want to live a long time? Avoid any of the things that make it worthwhile.