Introduction

Inflammation is a condition that has been well known for centuries. The four principal signs -- redness, swelling, warmth, and pain -- make it fairly easily recognized. However, 'sub-clinical' inflammation can occur within the body at different sites, without any obvious symptoms or signs. And it's probably much more common than previously thought.

This type of inflammation is taking a more prominent position in the changes that eventually lead to coronary artery disease, the forerunner of heart attacks. Indeed, a blood test for subclinical inflammation that measures C-reactive protein (CRP) is likely to become as important as cholesterol measurements. CRP plasma levels, when elevated, are associated with a 2- to 5-fold increased risk of a heart attack or some other cardiac events. Raised CRP levels are also seen in people who smoke, are obese, have an increased sensitivity to insulin, and type 2 diabetes.

Regular exercise decreases CRP levels as well as the risk of heart attack. Does this mean that exercise reduces subclinical inflammation, which is a key step on the path to coronary artery disease? A new study done in women with various ethnic backgrounds provides more information on this.

The study

Three different ethnic groups of women were examined - African-American, Native-American and Caucasian. Fasting blood CRP levels were measured. Height and weight allowed body mass index (BMI) estimates. Waist size and resting blood pressure were recorded. The volunteers were exercised on a treadmill at a standard rate until they reached 85% of their age-predicted maximum heart rate as a cut-off point; their oxygen consumption during this time allowed their 'metabolic equivalent task' (MET) value to be calculated.

The BMI results were classified as normal (18 to 25), overweight (25 to 50) and obese (over 50). Waist measurements were classified as more than, or less than, 88 cm (34.5 inches). CRP levels above 0.19 mg/dL were called 'high-risk' levels.

The findings

There were 44 African American, 45 Native American, and 46 Caucasian women in the study. They were mostly middle-aged, overweight and had relatively few of the known risk factors for coronary artery disease (smoking, high blood pressure, raised cholesterol, etc.).

The women's CRP levels corresponded closely to how fit they were on the treadmill test, as well as their BMIs. On average, the African American women were considerably less fit (i.e. had lower METs) and had higher CRP levels than the other two groups:

	African Americans	Native Americans	Caucasians
Average METs	7.2	9.1	10.0
Average CRP (mg/dL)	0.43	0.25	0.23

After making allowances for age, BMI levels, smoking status and the presence of diabetes, it was clear that lower CRP values were linked with greater fitness in the Native American and Caucasian women, but not in the African American women. So-called 'high-risk' CRP levels were seen less often in women who were physically fit.

Comments

The findings in this study confirm much of what has already been shown to be the case in men. And therefore they reinforce the likely benefits of physical fitness in women of different ethnic backgrounds. A larger study would probably show that African American women have a similar relationship between fitness and CRP levels as Native American and Caucasian women.

Why are CRP levels lower in fit individuals? It may be because fitness improves the body's resistance to infections, so that 'subclinical' virus infections cannot become established. Fitness also improves insulin sensitivity, reduces body fat, and lowers cholesterol levels. It may be that these factors are important for the reduction in CHD without any involvement of the CRP. Further studies will be necessary to clarify this.

Measuring CRP is emerging as an important step in helping to predict coronary artery health, as well as the conditions of other arteries in the body. Some people think that it may replace blood cholesterol levels in importance. It's true usefulness will surely become apparent from ongoing clinical and laboratory studies in the next year or so.