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Published: 2022-06-01 Updated: 2023-10-03, 13:22

Environments that can affect breast cancer

PROFILE Every day we are exposed to substances in our environment that can affect the expression of our genes, and in the short or long term cause both cancer and other diseases. Sophia Harlid studies environmental exposures that impact us during sensitive time periods.

Text: Lena Åminne
Image: Mattias Pettersson

Sophia Harlid studies the connection between genetics, the environment and health, but the road here has not been straight forward. Sophia studied molecular biology, first in Gothenburg and later in Lund. After graduation, she began a doctoral education with a research group that mainly dealt with human papillomavirus and cervical cancer. But circumstances made her change her focus and the resulting dissertation centered on small genetic differences that increase the risk of breast cancer.

Her continued research then took a slightly new direction – she wanted to investigate whether environmental exposures that affect the function of genes, e.g. by turning them on or off via epigenetic mechanisms, can be linked to cancer development. She got a postdoctoral position in the United States, in North Carolina, and moved there with her husband and two children - the family remaining for five "tremendously valuable" years.

An interesting meeting at a conference in Washington DC led Sophia and her family to Umeå. There she met Umeå researcher Bethany Van Guelpen and it turned out that they have related research interests - risk profiling and methods for finding people who are at risk of developing cancer.

Endocrine disrupting exposures

What particularly interests Sophia is how the environment affects us during especially sensitive time periods– such as during pregnancy and fetal life. One of her projects is about identifying women - younger than 50 years old - who, due to the environmental impact during pregnancy, have an extra high risk of developing breast cancer. With early preventive measures and an active reduction of hazardous substances in the immediate environment, there are good opportunities to reduce the number of people affected by this type of breast cancer.

The amount of small particles in the air can increase the risk of developing disease

“Smoking is one of the dangerous exposures that we know the most about”, says Sophia Harlid, researcher at Umeå University. “But there are many more substances in our environment, such as those that affect hormone receptors, so-called endocrine disruptors. They can be found, among other things, in various plastics, pesticides and cosmetics. The effects of these substances are often difficult to measure and the consequences of exposure are often not noticeable until after many years.”

Air pollution is also an example of an environmental exposure that Sophia and her colleagues are looking at, mainly by using registry data. There are, says Sophia, studies that show that the amount of small particles in the air can increase the risk of developing disease.

“Often the increase in risk is small for the individual. There can be many different and small risk factors that exert different effects. For me, it's important to identify when in life different exposures impact us the most. If we then can use that information to identify women who are at high risk early on, there is much that can be influenced. Examples of this could be increased awareness of having a high risk, starting screening earlier and easier access to the healthcare system if the need arises.”

Pregnancy – a sensitive period

During pregnancy, major changes occur in breast tissue, meaning that an unhealthy environmental impact could increase future cancer risk, more than at other periods in life. This because there is always a higher risk that mutations and other changes in the cells' genome occur when the cells divide a lot and even substances with weak carcinogenic effects can therefore have an impact.

The number of cases of breast cancer in younger women has increased, but it is still a rare disease.

“In addition to environmental exposures, pregnancy itself is a risk factor for early breast cancer” Sophia says. “Most often, pregnancy and breastfeeding are considered protective against breast cancer, and this is true for cancer that occurs after the woman undergoes menopause. But for breast cancer that occurs before the age of 50, the connection is often the opposite, depending on when the woman gave birth to her last child. It is important to remember that breast cancer before and after menopause are actually very different diseases, with different risk factors.”

With each pregnancy, the risk of breast cancer increases – however, this increase is not permanent but decreases over time. After a number of years, a woman who has been pregnant will again have the same risk as a woman who has never been pregnant and eventually the risks will intersect and the woman who has given birth will subsequently have a lower risk for the rest of her life.

“We know that with pregnancy, the risk of breast cancer increases because the breast tissue changes quite radically during these months. If the woman is also exposed to environmentally hazardous substances during that period, the risk could increase even more, which is what we want to investigate in several of my ongoing studies”.

Impact during the fetal stage

Another study Sophia Harlid participates in is NorthPop - a research study in Västerbotten with healthy and prosperous children as the goal. During fetal life, we are exposed to many kinds of exposures, several of which may have an impact on our future health.

“By analyzing blood collected from pregnant women as well as blood taken from the baby's umbilical cord, I try to identify environmental contaminants that are common during the fetal stage and understand the mechanisms explaining why some children developing asthma and allergy early in life”.

Some children are more sensitive to harmful substances than others

The goal is to map different exposures of environmental pollutants and find biological markers (in the form of epigenetic differences, see the fact box below) in the child's blood that may be early indicators of an increased risk of asthma and allergies.

“If we can find the environmental factors that increase the risk of asthma and allergy the most and understand how they affect the epigenetic profile of the child, we can hopefully explain why some children are more sensitive to harmful substances than others. Then the next step will be to investigate whether early interventions could mitigate or delay asthma and allergy development in these children”.


The genome refers to the DNA in a cell. Each cell needs to have certain genes turned on in order to perform its tasks, but which genes are off or on depends on the type of cell (for example, a kidney cell has other genes activated than a liver cell).  

The mechanisms that cells use to control and switch genes on and off are called epigenetic mechanisms, these mechanisms modify the genome without changing the genetic code.  

Epigenetic mechanisms play a key role in fetal development because, by regulating which genes are turned on or off, it controls which cells should develop into kidney, liver, and which ones should form brains, muscles, skin, etc. During this period, the fetus undergoes a so-called epigenetic reprogramming of all cells, which may make the fetus extra sensitive to external environmental influences. It can be food, stress, physical activity, chemicals, or other lifestyle and environmental factors. Environmental factors that affect the epigenetic profile during the fetal stage could therefore also affect the child's later health, both positively and negatively.  

Epigenetic changes are associated with cell division, but unlike mutations, changes in the genetic code, not all of them are permanent and they can be altered by, for example, lifestyle.

More about Sophia Harlid

Family: Husband and two children  
Coming from: Borås
Lives: Umeå
Drives me in the work: I want to be able to make a difference, working on projects that can lead to actual change is important to me.
Inspires me: People who struggle with, and overcome, difficulties in life.
Best relaxation: Likes to read and travel, meeting new people with shared interests and ideas.