People who have high levels of uric acid in their blood may have an increased risk of dying from heart disease. The presence of elevated uric acid identifies a sign of greater risk of cardiovascular mortality. The power of that effect -- the effect size -- is greater in women than in men and considerably greater in African Americans than in whites.
Previous studies have suggested that high levels of uric acid in the blood might be linked to heart disease, but the current study is the first such study to involve a nationally representative sample of people. In this very large study, uric acid levels were measured in nearly 6,000 people aged 25 to 74, who were then followed for an average of more than 16 years.
Researchers divided the participants into four groups based on uric acid levels. The lowest group's level was below 5.4, the second between 5.4-6.1, the third between 6.1- 7 and the fourth was above 7. They found that women who had the most uric acid in their blood were three times more likely to die from heart disease than those with the least.
Among men, the risk was 77% higher in men with the highest levels compared with those with the lowest levels. The risk of dying was higher in blacks than in whites, with black women having the highest increase in rates, the researchers report.
But in both men and women, the relationship between uric acid and heart-related deaths was only present in people aged 45 and older. People aged 45 to 54 who had high levels of uric acid appeared to have the highest risk.
Many, but not all, epidemiological studies have suggested that serum uric acid is a risk factor for cardiovascular disease. Increased serum uric acid levels are linked to obesity, distorted cholesterol levels and high blood pressure (when all three are present this is known as syndrome X), all of which are also associated with increased risk for cardiovascular disease.
Uric acid is a byproduct of the continual process in the body where old cells are broken down and new ones are formed. Normally, the acid is eliminated from the body in urine. Uric acid is the major product of purine metabolism and is formed from xanthine by the action of xanthine oxidase.
After menopause, values for women increase. In adults uric acid levels vary with height, body weight, blood pressure, kidney function, and alcohol intake. Uric acid concentration is influenced by the rate of production on the one hand, and the rate of elimination on the other. The changing level of serum uric acid concentration in women at menopause suggests an interaction with sex hormones.
Besides gout, elevated uric acid is related to a variety of other conditions including increased alcohol consumption, obesity, diabetes, high cholesterol, high blood pressure, kidney disease, heart disease, and water pill use.
More recently, it has been noted that the main reason uric acid is elevated is due to insulin resistance. The increase in serum uric acid levels may be an expression of an insulin-resistant state. This is supported by evidence that increased uric acid levels correlate with decreased insulin-stimulated glucose uptake and increased plasma insulin response to oral glucose loading.
The Journal of the American Medical Association May 10, 2000;283:2404-2410