Having older siblings has been linked to a higher risk of early-onset colon cancer in a first-of-its-kind analysis.
New York researchers found that people with more older brothers or sisters were also more likely to develop the disease before age 50, regardless of other risk factors.
The analysis of data from 500,000 adults excluded other variables known to increase the risk of colon cancer, such as family history of the disease, body weight and tobacco use.
The research simply shows an association and cannot say for certain that the two factors are linked, but scientists have said the “surprising” link is at least plausible.
Researchers in New York City found that people with two or more older siblings were 1.5 times more likely to develop early-onset colorectal cancer than those with no older siblings.
The chart above shows that colon cancer cases among those under 50 rose by more than 5,500 in 20 years. There is a drop in 2020 because the Covid pandemic caused fewer people to come forward for screening.
One theory is that younger siblings are exposed to more childhood illnesses when there are many brothers and sisters around, such as stomach viruses, which can cause inflammation and damage to the gut from an early age or change it in some way.
It also increases the likelihood of being prescribed antibiotics, which are suspected to play a role in the formation of bowel cancers, the researchers said.
Another hypothesis is that parents who have multiple children increase the risk of passing on genetic mutations that increase the risk of cancer.
The analysis was published in the journal Clinical Gastroenterology and Hepatology as a research letter, meaning it is not a full study.
As such, it did not look at other risk factors that could drive colon cancer, including diet and alcohol consumption.
Researchers from three New York City institutions, including Memorial Sloan Kettering and Columbia University, collected data from 500,000 UK residents included in the UK Biobank database.
There were fewer than 200 cases of colon cancer in that group, which could also have affected the results.
But the team found that people with two or more older siblings were 50 percent more likely to develop early-onset colorectal cancer than those who had none.
Additionally, people with an older sibling followed closely behind, being 40 percent more likely.
There was no association between colon cancers in people over 50 years of age and the number of siblings they had.
The team said “the factors driving the observed association are unknown,” although it offered several theories.
Mainly, they believe that having multiple older siblings increases exposure to a variety of childhood illnesses, such as the flu, chickenpox, and strep throat.
The team wrote: ‘CRC (colorectal cancer) can take decades to develop.
‘Therefore, it is important to understand the role of early life factors such as socioeconomic status, paternal age, genetics and microbiome composition.
‘Older siblings can be direct sources of microbiota (bacteria) seeding, and recent data show a positive association between the number of older siblings and greater diversity of the gut microbiome.’
The team went on to say that if their theory is true, this would increase exposure to antibiotics to treat bacterial infections.
Recent research suggests that drugs may be partly responsible for the rise in colorectal cancer.
Dr. Suneel Kamath, a colorectal cancer oncologist at the Cleveland Clinic, previously told DailyMail.com that overuse of these drugs could disrupt the gut microbiome, a network of healthy bacteria that helps regulate gut and immune health, among other functions.
“What we suspect is happening is that when there is overuse of antibiotics, there is a shift in what was a normal, healthy microbiome, and then bad pathogens are introduced in there, so to speak,” he said.
‘These can cause inflammation or other things that cause mutations in cells.
‘(This) can lead to an over-acceleration of cell division and replacement, and when that happens faster than it should, it can lead to mutations and, as a result, the formation of tumors.’
In one 2021 Study Reflecting the entire population of Sweden from 2005 to 2016, researchers identified more than 40,000 cases of colorectal cancer (CRC) compared with a matched control group of 200,000 cancer-free Swedes.
Both women and men who took antibiotics for more than six months had a 17 percent higher risk of developing cancer in the ascending colon, the first part of the colon where food reaches after the small intestine, than those who were not prescribed any antibiotics.
In addition, the researchers noted that people with more older siblings might be at higher risk because their parents were older when they had them than their siblings, as older populations are more likely to get colorectal cancer. However, they noted that more research is needed to confirm this.
The team has not confirmed whether the full study will be published. “The findings warrant confirmation in other, larger study populations,” the team wrote.
Dr Jen Dunphy, an oncologist at the Wellness Innovation Network in California who was not involved in the research, told DailyMail.com that while it seemed strange, the research is plausible.
She noted that one theory behind the findings is that older children bring more processed foods into the home.
“Typically, as children get older, they have more access to sugary drinks and processed foods both at school through their peers and at home, and often these snacks are shared between siblings, exposing younger siblings to these dietary risk factors for colorectal cancer,” she said.
However, he noted that further research would be needed to confirm this.
Responding to the new findings, Dr Kamath, who was not involved in the research, told DailyMail.com that the research is “very surprising” and “it’s difficult to know what the cause could be”.
One theory, he suggested, is that younger siblings are born with older sperm and eggs than their older siblings. This increases the risk of genetic mutations, which “could persist in the child and perhaps lead to cancer at an earlier stage in life.”
“I would add that this finding is not particularly useful because we cannot go back in time and ‘birth’ older siblings and I doubt that many people in the future will limit the number of children they have based on these findings,” he said.
‘It may be helpful for young people who have symptoms suspicious for colorectal cancer; perhaps their doctors, if they are aware of these findings, could refer them for a colonoscopy earlier if they are the youngest children in the family.’
‘Larger and better studies are needed to confirm whether these findings are true or not.’
Although the findings seem strange, the paper is part of a growing body of research suggesting that birth order and genetics may increase the risk of certain diseases.
TO review A study of more than 238,000 people in 17 countries, for example, found that children whose grandparents were obese were twice as likely to be obese or overweight themselves compared to those with more normal BMIs.
And a study in the Journal of epidemiology and community health They found that firstborns were significantly more likely to be overweight or obese than their siblings.