Garlic is powerful stuff. Able to ward of vampires, over-amorous admirers and, apparently, fleas. With that kind of might behind it, you would expect that including it in your diet might have some benefit for arthritis, so Arthur has been looking into it.
The chemical that gives garlic it's powerful smell is called 'allicin' and it's this compound that is thought to give garlic it's other benefits. Garlic has been shown to be effective in helping reduce high blood pressure and help prevent stomach and bowel cancers. It also has powerful anti-fungal, anti-bacterial and anti-viral properties.
It's effectiveness in helping arthritis is less clear: there is some recent and promising evidence to suggest that women who consume garlic (and related leeks and onions) are less likely to suffer from early osteoarthritis of the hip. In rheumatoid arthritis, it's usefulness is even less clear. I found one Russian study claiming that a compound made with garlic was as effective as other treatments, but the study was very small and is 12 years old...
Regardless, garlic is certainly a good healthy addition to your diet and a tasty one at that. If you find it very pungent, it might be worth trying to slice in rather than crush it. When you crush garlic you break the cell walls so more allicin is released creating that powerful flavour. Slicing it results in a milder flavour.