American Journal of Epidemiology Advance Access originally published online on September 4, 2006
American Journal of Epidemiology 2006 164(9):917-918; doi:10.1093/aje/kwj305
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Letter to the Editor |
RE: "CIGARETTE SMOKING AND INCIDENCE OF FIRST DEPRESSIVE EPISODE: AN 11-YEAR, POPULATION-BASED FOLLOW-UP STUDY"
36 Ridgewood Circle, Wilmington, DE 19809
(e-mail: celiamaryross{at}aol.com)
Klungsøyr et al. (1
) found an increased risk of depression associated with smoking. They attributed this to the inhibition of monoamine oxidase B-affecting neurotransmitters such as serotonin (1). They also examined alternative explanations, including selection bias, recall bias, unmeasured confounding variables, indirect causation, and reverse causation.
Tobacco smoke increases cancer risk through multiple molecular mechanisms (2, 3). It is not inconceivable that smoking might increase the risk of depression though multiple mechanisms as well.
DNA methylation, the addition of a methyl group to cytosine in the dinucleotide sequence 5'CpG, plays a role in silencing gene expression (4). A study of monozygotic twins found that epigenetic markers shift throughout the life span (5), suggesting that they may be influenced by the environment into adulthood.
Aberrant DNA methylation has been suspected of contributing to a number of psychiatric disorders, including depression (4). Findings of recent studies are consistent with the idea that aberrant methylation of DNA may play a role in depression. In a rat model, environmental factors produced a difference in DNA methylation status which correlated with differences in behavioral response to stress (6). Low folic acid levels result in aberrant methylation of DNA (4). Low folic acid levels have also been associated with increased risk of depression. Arsenic increases bladder cancer risk by promoting aberrant methylation of DNA (3). Higher levels of arsenic (
2 µg/liter) in drinking water have been associated with an increased incidence of depression (7). Smoking increases cancer risk in part by promoting the aberrant methylation of DNA (3). Now, Klungsøyr et al. have found that smoking increases the risk of depression (1).
A more basic question is: Since aberrant methylation of DNA has been suggested to be involved in psychiatric disorders ranging from schizophrenia to depression, do certain carcinogens that cause aberrant methylation of DNA also increase the risk of psychiatric disorders through that mechanism (3, 4)?
ACKNOWLEDGMENTS
Conflict of interest: none declared.
References
- Klungsøyr O, Nygård JF, Sørensen T, et al. Cigarette smoking and incidence of first depressive episode: an 11-year, population-based follow-up study. Am J Epidemiol 2006;163:421–32.
[Abstract/Free Full Text] - Shields PG. Epidemiology of tobacco carcinogenesis. Curr Oncol Rep 2000;2:257–62.[Medline]
- Marsit CJ, Karagas MR, Danaee H, et al. Carcinogen exposure and gene promoter hypermethylation in bladder cancer. Carcinogenesis 2006;27:112–16.
[Abstract/Free Full Text] - Abdolmaleky HM, Smith CL, Faraone SV, et al. Methylomics in psychiatry: modulation of gene-environment interactions may be through DNA methylation. Am J Med Genet B Neuropsychiatr Genet 2004;127:51–9.[Medline]
- Fraga MF, Ballestar E, Paz MF, et al. Epigenetic differences arise during the lifetime of monozygotic twins. Proc Natl Acad Sci U S A 2005;102:10604–9.
[Abstract/Free Full Text] - Fish EW, Shahrokh D, Bagot R, et al. Epigenetic programming of stress responses through variations in maternal care. Ann N Y Acad Sci 2004;1036:167–80.[CrossRef][Web of Science][Medline]
- Zierold KM, Knobeloch L, Anderson H. Prevalence of chronic diseases in adults exposed to arsenic-contaminated drinking water. Am J Public Health 2004;94:1936–7.
[Abstract/Free Full Text]
CiteULike 
Connotea 
Del.icio.us What's this?
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||