Studies presented at this month's meeting of the American College of Rheumatology offer some clues as to why gout, an inflammation of the joints, has been steadily on the rise since the 1960s.

Gout is characterized by pain, swelling and redness. It occurs most often in the big toe, but can also occur in other joints. This inflammation isn't constant; it flares up in discrete attacks, usually without warning. The inflammation and pain can be extreme and are caused by uric acid accumulation in joints. This can happen either because the body is producing too much uric acid or because the kidneys aren't removing enough of it.

Women who drank at least one drink of sugar-sweetened soda a day had a 74% higher risk of gout than those who drank the least soda (less than one serving per month).

Conditions such as high blood pressure and obesity increase the risk of suffering from gout. Use of diuretics (water pills) to control high blood pressure also increases the risk of gout, because they raise the level of uric acid in the blood. All three of these factors have been increasing for decades. Excessive alcohol use — generally more than two drinks a day for men and more than one for women — also increases the risk of gout.

Traditionally, gout has occurred much more often in men than in women because men generally have a higher blood level of uric acid. That's still true but may be changing as people live longer. That's because uric acid levels in post-menopausal women rise to nearly the level found in men.

The first of the three studies presented by researchers at the Boston University School of Medicine looked at what little information is available on the incidence of gout in the last 20 years. To obtain an estimate, the researchers compared information about gout contained in two national nutrition and health surveys, NHANES III from 1988-1994 and NHANES 2007-2008.

When rates in the most recent survey (2007-2008), were compared to the incidence reported in the 1960s, the incidence of gout rose to 3.8% of the population, an increase of 44% in less than two decades.

The second study dealt with the effect drinking fructose-rich beverage like sodas, have on gout. Fructose consumption raises the body's uric acid level; it's the only sugar known to do so. This study looked at gout occurring among nurses in the Nurses Health Study, a U.S. study that spanned 22 years (1984-2006) and had over 79,000 participants.

Women who drank at least one drink of sugar-sweetened soda a day had a 74% higher risk of gout than those who drank the least soda (less than one serving per month). Findings were similar for orange juice; a 41% higher risk of gout among those who drank one glass a day and a risk more than double (2.4 times) for those who drank two glasses a day, when compared to those who drank one glass (6 oz) or less per month.

This high increase in risk didn't translate into very many cases of gout, because the occurrence of gout in women in general and the women in the study in particular is low. There were only 778 total cases of gout in the study participants, a frequency of under 1%. That's much lower than the national average. The researchers calculated that drinking two glasses of orange juice a day compared to one could lead to 47 new cases of gout per 100,000 women yearly.

While the study did not include men, it's likely that men would benefit more than women from watching their intake of sugary beverages, because they're more susceptible to gout in the first place.

The third study dealt with the effect of caffeine on gout. Previous studies have indicated that caffeine consumption in general lowers the risk of gout. But those studies were conducted on the general population. This one looked specifically at people with a history of gout.

It found that in the short term, an increase in caffeine could trigger gout attacks. One finding was that people who normally take in low amounts of caffeine more than tripled their chance of a gout attack when drinking six servings of caffeinated beverages a day. But habitual drinkers were not affected by a caffeine increase.

This doesn't contradict the earlier studies that suggested a protective effect from caffeine. It does indicate that abruptly adding caffeine to your diet increases the risk of a gout attack in the short term.

The researchers note that caffeine's chemical structure is similar to that of allopurinol, a drug that lowers uric acid levels. Allopurinol is effective at easing the symptoms of gout and preventing gout attacks in the long-term, but it can actually increase the probability of a gout attack in patients taking it for the first time. The researchers reason that caffeine may have a similar mode of action.

While the overall effect of caffeine on gout may still be murky, the study suggests that people who do have gout attacks shouldn't up their caffeine consumption.

All three studies were presented during the 2010 annual meeting of the American College of Rheumatology, held in Atlanta from November 6-11.