Published: 21-05-2024 11:01 | Updated: 21-05-2024 15:19

New IMM thesis on exposure via drinking water and risk of disease

Welcome to Emilie Helte's defense of the thesis "Exposures through drinking water and risk of chronic disease" on May 24.

Emilie Helte, IMM

Time: May 24, 9.15 AM
Location: Andreas Vesalius, Berzelius väg 3, Karolinska Institutet, Solna
Supervisor: Professor Agneta Åkesson, IMM
Opponent: Associate professor Cristina Villanueva, Barcelona Institute for Global Health

Tre questions to Emilie

What is the thesis about?

The thesis is about the relationship between a number of waterborne exposures that are widespread in drinking water across the globe and risk of chronic diseases. The exposures assessed in the thesis were fluoride, calcium, magnesium and disinfection-byproducts, and were linked to bone mineral density and incidence of fractures, cardiovascular disease and cancer, respectively. The thesis encompasses four prospective cohort studies and one systematic review and dose-response meta-analysis. 

Can you tell us about some interesting results?

In the first paper, we found that fluoride exposure through diet and drinking water, as well as fluoride measured in urine was associated with increased BMD and at the same time increased risk of hip fractures in postmenopausal women. This rather contradictory finding could be explained by that the bone that is formed following fluoride exposure is of insufficient quality. In paper II, we observed that a higher concentration of minerals in drinking water, particularly magnesium, was associated with lower risk of stroke in postmenopausal women. In paper III, IV and V, we focused our work on disinfection by-products in drinking water and risk of cancer. While we found no overall association with risk of bladder cancer, drinking water with high concentration of disinfection by-products was associated with a higher risk of proximal colon cancer in men. The findings of increased risk of colorectal cancer in men was confirmed in paper V, in which we systematically reviewed the scientific literature on disinfection by-products and cancer. Moreover, the results of the meta-analysis suggested that disinfection by-products were also associated with increased risk of bladder cancer, at exposure levels higher than those examined in paper III. 

What further research is needed in the area? 

Drinking water is the most important constituent of our diet, consumed by essentially everyone in the population daily. Yet, the knowledge of the health impact of many waterborne exposures is limited. Future studies on fluoride in drinking water should focus on finding the threshold when the potentially negative health effects of fluoride start to appear, to see if they overlap with those levels that are beneficial for oral health. 

Regarding the association of minerals in drinking water and cardiovascular outcomes, only few studies have focused on stroke, which is the outcome we found the strongest association with. More well-designed epidemiological studies are needed to corroborate our findings of a protective relationship. 

Disinfection by-products are a complex mixture of more than 800 substances. In the thesis, we assessed the relationship between trihalomethanes, which is only one group of compounds formed following chlorine disinfection. Other groups of compounds may be equally, or possibly even more strongly associated with cancer, but the epidemiological evidence for these substances as well as the evidence for other cancer outcomes than bladder and colorectal cancer is very limited. 

Read the thesis