(RxWiki News) The world is filled with various chemicals and substances that don't occur naturally in the environment. Scientists are continually trying to understand how these affect human health.
It's a tricky science, however, because it often relies on looking at broad populations and drawing conclusions based on links between a condition and a possible exposure to this or that chemical.
A recent study looking at links between fathers' occupations and birth defects occurring in their children found an association between a broad range of possible jobs and defects.
But nothing in the study could establish that a specific job might cause any specific defect.
"Talk to your OB/GYN if you have concerns about exposure to chemicals."
The study, led by Tania A. Desrosiers, an epidemiologist at the Gillings School of Global Public Health at the University of North Carolina, Chapel Hill, used data from the National Birth Defects Prevention Study.
The study included data from 9,998 babies who had one of 60 different types of birth defects and 4,066 babies who had no birth defects; all were born between 1997 and 2004.
The birth defects included congenital heart defects, problems with a baby's eye or ear, cleft palates and defects in the central nervous, gastrointestinal, muscular and skeletal systems.
The researchers interviewed the mothers of the children by telephone about the babies' fathers' jobs, which were then categorized into 63 different groups.
The groups were based on what kinds of things the fathers would likely have been exposed to in those specific jobs. Most of the fathers (90 percent) only held one job during the period of time that the researchers were asking about: from three months before conception to the first month of pregnancy.
Overall, their analysis uncovered over 100 links between a particular job and a particular defect, so they summarized their findings by looking at groupings of jobs and multiple defects.
They found that certain jobs held by fathers were linked to a higher rate of multiple birth defects in their children.
For example, photographers and photo processing workers were more likely to have children with one of three different eye defects.
The career of landscaper or groundskeeper was linked to three different categories of gastrointestinal defects.
The career with the most number of individual defects was artist; children whose fathers were artists were more likely to have eye or ear defects, cleft palates or defects in the gastrointestinal system.
The data related to artists was problematic, however, because none of the babies in the group without any defects had a father who was an artist, and some of the data revealed exceptionally higher odds of a birth defects among these men's children.
The researchers hypothesized that artists' media (which could be stored in the home) may be more likely to contain lead or organic solvents, both of which have been linked to birth defects in past studies.
Overall, the careers that were linked to multiple defects besides the ones above included mathematical, physical and computer scientists; food service workers; hairdressers and cosmetologists; office and administrative support workers; sawmill workers; petroleum and gas workers; chemical workers; printers; material moving equipment operators and motor vehicle operators.
Another one third of the jobs did not appear linked to any type of birth defect. These jobs included architects and designers; healthcare professionals; dentists; firefighters; fishermen; car assembly workers; entertainers; smelters and foundry workers; stonemasons and glass blowers or cutters; painters; train drivers and maintenance engineers; soldiers and commercial divers.
The study was large and broad but was not able to determine the specific exposures fathers may have had to specific chemicals or other agents. Further, the study only identified associations, or links, between a father's career and specific or multiple birth defects.
Nothing in the study can show that a father's career caused any specific birth defect. Further, the authors did not discuss possible confounders, which are characteristics of a person that may be able to partly or fully explain a result in the data when it is taken into account, such as health histories of the fathers or their demographics.
The mathematical analysis used by the researchers also could have led to inflated numbers if there were only a small number of some occupations represented (such as the fact that none of the babies without defects had artist fathers).
"Ultimately, observed associations should be interpreted with caution, as our study is limited to using occupational groups as a surrogate measure for workplace exposures and exposure mixtures potentially encountered at each job," the authors wrote.
In other words, the researchers used categories of jobs to estimate what kinds of exposures to certain chemicals the fathers might have had and then compared them to the rate of birth defects in their children.
The study was published July 17 in the journal Occupational and Environmental Medicine. The research was funded by the Centers for Disease Control and Prevention and the US National Institute of Environmental Health Sciences. The authors declared no conflicts of interest.