If you're smart, you think about your knees a lot. They're crucial to lifting, to running, to almost every sport, and they're worth taking good care of. (If you're lucky, you don't have to think about your knees at all; they just work. But not all of us are that lucky.)

So if you love your knees--and all your other joints--why not take glucosamine and chondroitin? Those are probably the best known supplements for joint health, but are they worth it? Do they actually do anything?

Joint Health

First, let's talk about this nebulous concept of "joint health." It sounds like a good thing. But what does the average lifter have to be concerned about? A study of Olympic weightlifters done at the actual Olympic Training Center in 1999 found that the lower back, knees, and shoulders were the most common sites of injury. However, back and shoulder injuries were mostly muscle strains and 85 percent of the knee injuries were diagnosed as tendonitis.

"The injuries typical of elite weightlifters are primarily overuse injuries, not traumatic injuries compromising joint integrity," the authors wrote. None of these are things that glucosamine and chondroitin will help with.

But over time, lifters can end up with osteoarthritis. Once known as "wear-and-tear" arthritis, it's associated in athletes with both heavy load bearing and injuries to the knee, but it's most likely the injury and not the loading that is the real culprit. Meniscus tears in particular are associated with arthritis, although the details of that link are still up for debate.

The Supplements

Both glucosamine and chondroitin are natural chemicals involved in the body's process of making cartilage. The surfaces of your joints that rub together are lined in cartilage. If you give your body more of the building blocks, the idea goes, this might help with cartilage repair or at least slow down its degradation in conditions like osteoarthritis.

This is just a guess, though, and scientists still aren't sure of how it works, assuming that it does work at all. One problematic fact: there's a thousand times more glucosamine in your body already than in the pill you're taking, so it's hard to see how the pill could possibly help. Science Based Pharmacy lays out these and more reasons why you should be skeptical of the idea that these supplements help joint health.

A disclaimer: Glucosamine and chondroitin are regulated as supplements, not drugs, in the US, so the fact that you can buy them doesn't guarantee that they work. Supplements don't have to pass any tests of safety or efficacy before they hit the market, and while the FDA limits what claims companies can make about supplements--hence the little disclaimers about not being meant to treat or prevent disease--they don't get to pre-approve labels, either. Bottom line, lots of crap is being sold without a shred of evidence that it does what it says on the label. So the fact that you can buy a joint health supplement doesn't mean that what's inside is actually good for your joints.

A good place to begin understanding whether a supplement works is to take a look at evidence summaries like the ones at Mayo Clinic or Medline Plus Supplements. Here's one on glucosamine and one on chondroitin. While a variety of claims have been made about these, the best evidence is for symptoms of knee osteoarthritis. Mayo Clinic gives a grade B for glucosamine, grade A for chondroitin.

The truth is, it's complicated. There are studies that show a small beneficial effect of glucosamine and/or chondroitin, and there are others that don't. Some use glucosamine sulfate and some use glucosamine hydrochloride; in theory they should be the same, but studies that use the sulfate are more likely to turn up positive results. There's even a theory that it's the sulfate rather than the glucosamine that is good for your joints. Studies by independent groups have also found smaller effects compared to studies funded by supplement companies.

Overall, the biggest meta-analyses say that the supplements work. Here's the catch, though: they don't work very well. Glucosamine, for example, outperforms a placebo in most studies, but it's not like patients are thinking, "hmm, should I take glucosamine, or should I take a sugar pill?" Rather, it's "should I buy the giant bottle of glucosamine and take it every day, or should I just pop a Tylenol when it hurts?" And in fact, the effect of glucosamine, as measured by arthritis symptoms and pain, is similar to the effect of drugs like Tylenol.

In one clever trial, people with osteoarthritis who were already taking glucosamine, and said it helped, allowed researchers to mess with their medicine. The scientists kept half of the patients on their regular supplement, and switched the other half to a placebo with no glucosamine at all. Both groups did equally well, suggesting that while glucosamine may help, you could save money by switching to, say, tic tacs. (Glucosamine's sales reportedly total $2 billion worldwide.)

A study earlier this year took a different tactic: rather than asking patients how much their knees hurt, they ran their knees through an MRI to look at how much cartilage damage they had before and after taking glucosamine for almost six months. (Interestingly, the study was sponsored by Coca-Cola. The supplement and placebo were given as lemonade-flavored drinks.) There was no difference, although critics point out that six months may not have been long enough.

Bottom Line

I fall on the skeptics' side, but the jury is clearly still out. The good news is that neither glucosamine nor chondroitin is associated with any serious side effects, so if you take it and feel better, or even think you feel better (hey, use that placebo effect to your advantage), then maybe it's worth it.