Eating fish is supposed to be healthy but many people are concerned about mercury in their diet. A recent study tested the toenails of over 170,000 men and women as a method of determining whether mercury consumption contributes to heart disease. Nail testing is an accurate way to check for heavy metal levels in the body such as lead, chromium, arsenic and mercury as nails are so slow growing they can give information about exposure to chemicals that occurred many months in the past.
This study, reported in the New England Journal of Medicine on March 21, 2011, combined data from two studies where toenail clippings were collected over a period of 11 years. Of those persons tested, 3,427 cases were identified as having cardiovascular disease (coronary heart disease and stroke). They were then compared against another set of controlled participants who were matched in risk level according to age, sex, race and smoking status. Other information about lifestyle, additional risk factors and amount of fish regularly consumed was gathered by questionnaire.
Mercury and selenium levels were measured in the toenail clippings. Researchers determined through calculations that participants with higher mercury exposure did not have a higher risk of cardiovascular disease. No connection of selenium levels and heart disease was found either.
Concerns over exposure to high levels of mercury are not unfounded in relation to other health conditions. Mercury, in the form of methylmercury, is poisonous to the nervous system and has the greatest risk to the developing brain of an unborn child. This is why pregnant women are cautioned to limit their intake of fish. There have been reports of mercury causing cancer but the studies have not been conclusive. Exposure to mercury as a vapor and other forms of mercury compounds pose other health risks but one would need to be exposed high levels for symptoms to develop.
Mercury is naturally present in rocks, soil and coal. As coal is burned for power, mercury is released into the air and settles into water. Plankton absorbs the mercury, which is then eaten by small fish.