ScienceDaily (May 14, 2009) — Individuals exposed to relatively higher amounts of formaldehyde had a higher rate of death due to blood and lymph system malignancies than those exposed to lower levels of formaldehyde in a large cohort study.

In the National Cancer Institute's formaldehyde cohort, which was previously followed through 1994, formaldehyde exposure was associated with an increased risk of leukemia. In the current study, Laura Beane Freeman, Ph.D., of the NCI in Rockville, Md., and colleagues, extended the follow-up through 2004. The cohort includes 25,619 individuals exposed to formaldehyde at work.

With a median follow-up of 42 years, the investigators observed a positive association between all lymphohematopoietic malignancies and peak formaldehyde exposure, with a 1.37-fold higher risk among those with the highest peak exposures compared with those with the lowest level of peak exposures. There was no statistically significant association with cumulative exposure or average intensity of exposure. An excess risk was seen for several sub-types of these malignancies, most notably myeloid leukemia, with a 1.78-fold higher risk. Myeloid leukemia is the type most often associated with chemical exposures. The level of increased risk was highest earlier in the follow-up period and then declined steadily over time such that the cumulative excess risk no longer reached statistical significance.

"In the current follow-up, the overall risk of myeloid leukemia has declined from our previous report, but remains somewhat elevated. While that time trend may suggest that the previous excess risk estimates were due to chance, the pattern is consistent with a possible causal association, with the largest risks occurring closer in time to relevant exposure," the authors write. "It is our opinion that the overall pattern of risks seen in this extended follow-up of formaldehyde workers, while not definitive, warrants continued concern."

This research was published in the Journal of the National Cancer Institute May 12, 2009.

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