The findings from a new study have suggested that life-long, low-level lead exposure is associated with increased reports of depression and anxiety that are related to phobias in older women. The research was published recently in Environmental Health Perspectives. The associations were strongest for premenopausal and postmenopausal women who regularly took hormone replacement therapy. The results suggest that mental health may suffer from long term exposure to low levels of lead. The levels measured in the women were at or below the level of concern set by the U.S. Centres for Disease Control. The majority of research on the toxic effects of lead focuses on early life exposure and high occupational exposure. This is one of the first studies to investigate the cumulative effects of lead on mental health at levels routinely experienced by adult women. For most people, typical exposure to lead comes from the environment. Even though lead’s use in commercial applications has decreased, people continue to be exposed from paint in older homes and buildings and contaminated dust and soil. Air and water can also contain lead from industrial sources and plumbing materials. Lead can adversely affect many parts of the body, including the brain, the nervous system and the cardiovascular system. It is known to affect memory, intelligence and motor skills. Because of these effects, exposure is a risk factor for cardiovascular disease and mood disorders, such as depression and anxiety. A recent study links lead exposure to pessimism in men. Studies in the workplace show that exposures to higher levels of lead are related to motor, cognitive and mood disorders as well as other psychological symptoms. The connections in the general population are similar. A large-scale study from the National Health and Nutrition Examination Survey (NHANES) for 1999-2004 found blood levels of lead were associated with increased diagnosis of depression or panic disorder in younger adult men and women. That study measured blood lead levels and estimated short-term exposure. A few large studies have considered the link between low environmental exposure to lead and mental health outcomes in adults. Yet, only one of them included older women. Since mood disorders are twice as likely to be reported in women as men, there is a great need to determine the underlying factors of mood disorders in women of all ages. Although the connection is not well understood, experts are beginning to understand how lead influences mental health. One way is that lead affects hormone and stress pathways in brain regions involved in depression and anxiety. In addition, it influences the development of hypertension and other cardiovascular diseases that lead to depression. During the new study, the researchers from Harvard’s Public School of Health looked at the associations between cumulative lead exposure and the incidence of anxiety and depression in older women. They recruited 617 women aged 41 to 83 years old who were part of the larger Nurses Health Study that began in 1976. The women were not obese; had no history of major chronic disease; and were part of either a case-control study of lead exposure and hypertension or a study of lead exposure and osteoporosis. Bone lead levels were measured in the tibia and patella bones using x-ray fluorescence. Bone levels show a person’s lifelong lead exposure while blood levels can indicate short-term exposures. Lead remains in the patella or kneecap for years, whereas the amount of lead in the tibia or shinbone is estimated in decades. Questionnaires sent out via the nurses study provided psychological measures. The women completed mental health surveys for depression and for phobic anxiety of common fears, such as enclosed spaces, illness, heights and crowds. Bone lead levels were compared with the mental health survey scores. The researchers compared three groups: all women, premenopausal women on hormone replacement therapy (HRT) and postmenopausal women on HRT. They statistically considered factors that could influence the results, such as education, smoking and socioeconomic status. The results showed that lead levels in bone and blood were similar to those found in other large human studies. The amount of lead in the blood of the women was low about 2.3 micrograms per decilitre of blood (?g/dL). This is well below the 10 ?g/dL recommended level of concern set by the U.S. Centres for Disease Control and Prevention (CDC). The life-long exposure estimates from bone readings were also relatively low. Average lead level within the tibia was 10.3 ?g/g and in the patella was 12.5 ?g/g. These levels suggest the women were exposed to lead through everyday environmental exposure. As expected, lead levels increased with age, smoking and alcohol consumption. Depressive symptoms were worse with increasing amounts of lead in the entire group of women, but the associations were weak. Positive relationships were found for pre-menopausal women and postmenopausal women on hormone replacement therapy (HRT). In these groups, depression scores increased with increasing lead concentrations in the tibia. Adjustments for age, education, lifestyle and socioeconomic status did not affect this association. Similar results were found for lead exposure and anxiety symptoms. No associations were found between lead concentration and anxiety symptoms in the entire group. However, in premenopausal and postmenopausal women on HRT, lead levels correlated to feelings of anxiety. This is the first study to find associations between life-long lead exposure and depression and anxiety in older women. The links were strongest with women on hormone replacement therapy. The finding is important because women are twice as likely as men to suffer from depression. Furthermore, the low bone lead levels measured suggest the exposures are from everyday sources rather than job-related sources. The findings further confirm previous associations found between mood disorders and short-term lead exposure in large human studies. In the Normative Aging Study, higher lead concentrations measured in the blood of older adult men were associated with phobic anxiety and depression. Within the NHANES study, blood lead levels in men and women were associated with diagnosed major depressive disorder and panic disorder but not generalised anxiety disorder. One potential issue, the authors admit, is that menopause and the use of HRT could affect blood and bone lead measurements. During menopause, bone turnover increases. As this happens, more lead could leave the bone and be deposited in the blood. This turnover could produce similar blood lead levels in menopausal women as a non-menopausal woman and would artificially decrease the estimate of bone lead exposure in menopausal women. However, HRT reduces the bone turnover associated with menopause. These differences in bone dynamics could explain why the associations between bone lead levels and mood disorders were weak in menopausal women not on HRT and strong in pre-menopausal and menopausal women taking HRT.
Environmental Health News, 18 April 2012 ;