Studies show that friends can affect your health more than family.

People will strong social ties have a 50% better chance of survival, according to a clinical review of 150 studies and 300,000 people.

The key is to have a few very close friends you have strong connections with.

Want to live longer? Make close friends — because research shows that friends can affect your health even more than family. The 2005 Australian Longitudinal Study of Aging found that close relationships with children and other relatives had very little impact on how long you live, but people with the most friends tended to outlive those with the fewest by 22 percent.

Better yet, a clinical review of nearly 150 studies found that people with strong social ties had a 50 percent better chance of survival, regardless of age, sex, health status, and cause of death, than those with weaker ties. (The conclusion was based on information about more than 300,000 individuals who were followed for an average of 7.5 years.)

In fact, according to the researchers, the health risk of having few friends was similar to smoking 15 cigarettes a day, and more dangerous than being obese or not exercising in terms of decreasing your lifespan.

Keep in mind that means real friends. Not Facebook friends or Twitter followers. Not the guy in the office down the hall that you like to exchange Spinal Tap quotes with. (Not that there's anything wrong with that, of course.)

So do this. Take a second and list your friends.

Then think about whether the people you jotted down would include you on their lists of friends. Think you'll be on all those lists? Probably not.

In fact, only about half the time will the people you consider to be your friends consider you to be a friend. (And of course that also means that only about half the time do you consider someone who thinks of you as a friend to be your friend.)

Why? There are lots of possible reasons. One is that your definition of "friend" may differ from other people's.

And regardless of how you define "friend," according to Robin Dunbar you don't have the time to have dozens of friends. Because of that, Dunbar feels we have different layers or slices of friends: One or two truly best friends (like your significant other and maybe one other person), then maybe 10 people with whom we have "great affinity" and interact with frequently, and then all sorts of other people we're friendly with but who aren't actually friends. In total, Dunbar's Number says you can have about 150 people in your social sphere.

All of which means "friendly" and "friend" are two very different things.

And that means, if Dunbar is correct, that you can only have a handful of true friends. That means some people you think of a close friends don't see you that way at all.

So why — apart from making you and I wonder how people really feel about us — does this matter?

Superficial, distant, and less than meaningful relationships can lead to feelings of insecurity and loneliness, which can increase your risk of illness and death just as much as obesity, alcoholism, and smoking.

That means the key isn't to have more friends. The key isn't to try to have a tons of friends. The key is to have three or four really, really good friends, and then, of course, plenty of people who aren't necessarily friends but are fun to be around, or result in a mutually beneficial relationship, or share common interests.

You don't need to be less friendly. You just need to nurture the most important relationships in your life.

What's the easiest way to do that? Think about what you can do that will help the people closest to you be happier, and then do it.

You care about your casual friends, but with casual friends, "care" is a noun.

Real friends see "care" as a verb. They act on their feelings. They step in, step up, and sometimes step outside their comfort zone to do something selfless, just because they can.

If you want to have closer friends, make "care" a verb. Support. Encourage. Help.

And if you don't know how, ask — because real friends ask.