Can Too Much Running Increase Colon Cancer Risk?

Just when I'm reading about Ultras

If you've read a previous post of mine you know that there is evidence showing that people who are physically active have a lower incidence of cancer. A 2016 meta-analysis of 52 prospective studies found physically active adults were 24 percent less likely to have colon cancer compared to sedentary peers.

So I was very surprised when I came across a poster presentation that suggested that those who do high volume ultra marathon and marathon running may actually have an increased risk of advanced pre-cancerous colon lesions. The New York Times wrote about this too.

Researchers had 100 long distance runners ranging from 35 to 50 years who completed at least 2 ultramarathons (> than 50 km) or 5 marathons. These runners underwent screening colonoscopies, with all polyps reviewed by a team of oncologists, pathologists and gastroenterologists. 

They were found to have polyps (> 10mm with  tubulovillous features) that were more likely to turn into cancer compared to the general population (40-49 years old). 15 percent of the 100 runners had advanced adenomas. This was greater than 10 times higher than the benchmark. 39 runners had at least 1 adenoma of any type.  Prevalence in the matched general population was just 1.2 percent.

Most cases happened in runners with very high training exposure (pictured above), multiple ultramarathons or completed more than 15 races. There were even a few cases of high grade dysplasia, just 1 step away from colorectal cancer.

The researchers' hypothesis was that due to extremely high volume distance running, this leads to repeated low blood flow to the gut leading to chronic injury and inflammation. This can repeatedly injure the stomach lining. This recurring pattern may then accelerate carcinogenic changes that lead to the development of pre-cancerous adenomas.

Moderate exercise does lower systemic inflammation, but ultra marathon training can increase inflammation in the gut made worse with frequent high volume racing. This worsens during intense exercise in the heat. Since chronic gastrointestinal stress impairs absorption of fibre and micronutrients that normally protects the colon, their findings may be reasonable. More so if recovery isn't adequate.

The difference compared to the normal population does cause some concern. However, do note that this is a relatively small study done only in 1 location. There is no proof of causation, genetics, nutrition and other lifestyle factors that may also play a role. 

For most of us runners, running is protective against colon cancer, and does not increase our risk to it. I do not have any patients who run >2 ultra marathons or more than 5 marathons a year. If they do, then their risk profile may (emphasis on may) be higher. 

So if you do log mega mileage, race often and are concerned about your cancer risk, it may be wise to get colon cancer screening particularly if you have persistent gastrointestinal symptoms.

Do wait for the full peer review study to be published before making any final conclusions.

Reference (for the abstract)

Cannon TL, Bonomelli S, SwainWR et al 92025). Risk Of Pre-Cancerous Advanced Adenomas Of The Colon In Long Distance Runners. J Clin Oncology. 2025 ASCO Annual Meeting. 43(16) suppl. DOI: 10.1200/JC0.2025.43.16_suppl.3619

Are You A Fast Or Slow Walker?

Let's go for a walk

Walking seems like such a simple thing. We usually do not think about it until you cannot walk properly. My patient who had a recent ACL reconstruction literally had to learn how to walk again Pictured below).

Walking actually relies on quite a few body systems working together. Your eyes to help you see where you are going.  Your muscles and bones working together to get you places, your heart and lungs to circulate oxygen. Of course you need your brain and nerves to coordinate everything.

Previous studies have shown that walking speed is a significant predictor of life expectancy in older adults. Pooled results from 9 studies involving 34,000 adults aged 65 and older showed that walking speed was significantly associated with lifespan. Men with the slowest walking speeds at age 75 had a 19 percent chance of living for 10 years compared to those with the fastest walking speeds who had 87 percent chance of survival.

Another study found that even amongst healthy adults aged above 65, participants with slower walking speed were 3 times more likely to die of cardiovascular disease compared to those who walked faster.

Did you know that if you are a slow walker you may have a smaller brain compared to a faster walker? Research has shown that how fast you walk to the shops, MRT, or your local coffee shop can predict your chance of a heart attack, being hospitalised or even dying. Your walking speed can even reveal your rate of cognitive ageing.

As we age, these systems start to slow down. Studies show that walking speed is a significant predictor of life expectancy in older adults. This does not just apply to older adults as Rasmussen and colleagues (2019) found that even amongst 45 year olds, a person's walking speed can predict the rate at which their brain and body were ageing.

In that study (Rasmussen et al, 2019) had 904 subjects, all 45 years old born between 1972 and 1973 living in New Zealand. Their health and cognitive function were assessed regularly over their entire lifespans. 

There was fairly huge variation in walking speed among the subjects. You would think that these 45 year olds would have similar walking speeds but some walked as quickly as healthy 20 year olds while others walked as slowly as much older adults.

The 45 year olds with slower walking speeds showed signs of "accelerated ageing" with their lungs, teeth and immune systems were in poorer shape compared to those who walked faster. They also had 'biomarkers' associated with a faster ageing rate such as higher blood pressure, raised cholesterol and lower cardiorespiratory fitness. 

The slow walkers also had a weaker hand grip strength and found it more difficult to get up from a chair. Other signs of cognitive ageing include lower IQ test scores, worse memory test scores, processing speed, reasoning and other cognitive functions. MRI scans showed they had smaller brains and a thinner neocortex - the outermost brain layer which controls thinking and higher information processing.

Even the faces of the slow walkers were rated as ageing faster than the faster walkers!

The research suggests that the slow walkers' brains and bodies age at a faster rate compared to the quick walkers. There were already signs that these health differences were present from an early age  as researchers were able to predict the walking speed 45 year olds based on intelligence, language and motor skills test taken when the participants were just 3 years old. 

Wow, I am so surprised that there is a link between how fast people walked at 45 years old and their cognitive abilities all the way back to when they were 3 years old. Perhaps walking speed is not only a sign of ageing but a clue to lifelong brain health.

Reference

Rasmussen LJH, Caspi A, Ambler A et al (2019). Association Of Neurocognitive And Physical Function With Gait Speed In Midlife. JAMA Netw Open. 2:2(10): e1913123. DOI: 10.1001/jamanetworkopen.2019.13123.

Fit But Overweight Or Normal Weight But Unfit

Picture from Truenorthwellness

What if you were fit but overweight and even obese compared to being unfit but normal weight. Which do you think is better?

A new meta-analysis pooled results from 20 prospective cohorts thus investigating nearly 400,00 people (Weeldreyer et al, 2025). Participants were categorized by body mass index (BMI) as normal weight, overweight or obese. Their carodiorepiratory fitness (CRF) were measured by maximal exercise testing to determine if they were fit or unfit based on age adjusted VO2 max. This was to determine if BMI or CRF predicts mortality risk better.

This meta-analysis is different from earlier ones since it includes more women. It also has participants from a broader age range, geographic backgrounds and health status. Better statistics all round. Findings more generalizable and results more precise.

The reference group - normal weight and fit was compared to all other combinations. Compared to the reference group, those who were both overweight but fit and obese but fit, both groups had virtually the same risk of dying from any cause. About 4 percent lower and 11 percent higher respectively, which was not statistically significant. Being fit protected against being overweight and obese for all-cause mortality.

Not so good news for the unfit. Those who had normal weight but were unfit had a 92 percent higher all-cause mortality risk. The risk was similarly high for unfit and overweight (82 percent higher) and even higher for the unfit and obese (104 percent higher).

For cardiovascular disease mortality, the differences between weight categories were more pronounced. The fit but overweight had a 50 percent higher risk while those fit and obese had a 62 percent higher risk than fit individuals with normal weight. Note that neither was significant, although it meant that being fit protected one against the risk of dying from cardiovascular disease.

Now for those who were unfit for cardiovascular disease mortality, the numbers were not pretty, in fact they shyrocketed. 104 percent higher risk for normal weight, 158 percent for  overweight and 235 percent for the obese.

In short, being unfit more than doubled mortality risk for many cases, regardless of BMI, while being fit can netralize the impact of carrying extra weight.

These findings show that BMI alone is a weak predictor of health and improving cardiorespiratory fitness can cancel out much of the risks associated with a higher BMI.

Perhaps BMI is not a good indicator. One may have a high BMI and yet be muscular and fit - the Amercian football players in the NFL have high BMI values. They are classified as obese, but they are actually very fit and muscular.

Should we be more concerned with increasing fitness levels over weight loss during public health awareness? There seems to be more emphasis now on weight loss and eating less processed food rather than increasing physical activity. 

This study suggests boosting fitness levels should be at the top of the list, not just as a replacement for tackling obesity. Studies like this show that physical activity is definitely more important than diet for those who want to live to a ripe, old healthy age. Not to say that diet does not matter. But fitness is king. Perhaps our Ministry Of Health should angle some incentives?

Reference

Weeldreyer NR, De Guzman JC, Paterson C et al (2025). Cardiorespiratory Fitness, Body Mass Index And Mortality: A Systematic Review And Meta-Analysis. BJSM.59:339-346. DOI: 10.1136/bjsports-2024-108748

Aircon Mall Marathon

Picture from Arabnews

I remember meeting some Singaporeans who lived in Doha when Team Singapore went to compete in the 2006 Asian Games. They told us during the hottest months temperatures went up to over 50 degrees Celsius. How can one exercise safely I remember asking myself back then.

Well, while Singapore celebrates turning 60 on August 9th, 2025, a sprawling shopping centre in Dubai organized a "Mallathon" on the same day.

Back by the Dubai government, it aims to encourage exercise during the hottest month in United Arab Emirates (UAE). They make use of Dubai's giant malls which are otherwise empty at that time. 

Runners can take part in organized 2.5km, 5 km and 10 km races at designated malls complete with podium presenattions and prizes.

One can also wait in line to use electric bikes that powered blenders to make healthy smoothies after exercising.

Perhaps our Singapore malls can do the same. To help revive our ailing retail and food and beverage scene.

Happy National Day Singapore!

Are The Chinese Brands Surging Ahead?

My first observations about someone are always about their footwear. I have done this ever since I was a teenager, I would be curious about people's shoes. I always look at what shoes a person is wearing especially if they are a runner. Of course as a physiotherapist now, I do the same.

If you are a runner you may or may not have heard of Anta, Li-Ning, Qiaodan, Xstep. They were usually unheard of a few years ago and dismissed as inferior to Nike, Adidas, Asics and New Balance (sorry if your brand is not listed). 

However, Chinese Super running shoes with their carbon fiber plates and super foam are increasingly becoming mainstream compared to before. Selemon Barega (Tokyo Olympics 10 000 m winner) switched from Nike to Li-Ning 3 days before the race and won the 2025 Seville marathon in an impressive 2:05:15 hours.

Some Chinese running brands have already set up shops in Singapore. Li-Ning has 2 stores here while Anta now has 11 stores after opening their first in 2023.

There may still be perceptions of Chinese Super shoes as being lower quality and/ or durability. They are definitely cheaper costing between S$150-200 a pair compared to more than S$300 for Super shoes from established brands.

I have definitely noticed some of my patients using Chinese super running shoes. My patients say that they are not only cheaper than the established brands, they seem to have even more energy return and propulsion. Personally, I have not tried any of the Chinese running brands yet.

Not just with running shoes, it seems. If you happen to be a cyclist you may have heard of Winspace or X-Lab? Some cyclists still regard cycling tech from China as cheap and/or  counterfeit. Too good to be true or too dangerous to use because of high failure rate.

Cycling World Tour team XDS Astana is using a carbon fiber bike made by X-Lab. This is the last team Mark Cavendish, who has won the most stages in the Tour De France rode for albeit on a different bike before he retired last year.

Winspace wheels are much cheaper compared to Campagnolo, Enve or Lightweight wheels. Lightweight's Meilenstein Art wheels cost $8000 while Winspace's Lun Hyper go for $1500. At almost the same weight, with a deeper rim profile, it ticks all the boxes. Winspace wheels have even been rated as excellent by engineering expert Hambini. They are also UCI approved. Matter of time before they get used at a World Tour level race or even at the Tour De France.

Will I consider Winspace's wheels? I currently use Campagnolo's WTO 45mm Bora wheels on rim brakes. I am not a fan of disc brakes on road bikes. Personally, I think bicycles have gotten more expensive and more complicated with disc brakes. I am sure bike manufacturers like the higher margins that come along with them too. When it becomes impossible to find a rim brake wheelset from a mainstream brand I may have to switch to them since Winspaceare committed to supporting both disc and rim brakes.

See how cheap they are

I still look at cheap carbon wheels, shoes, ceramic pulleys on AliExpress and Shopee (above). For reference, my Ceramic Speed pulley wheels alone cost $500 a pair. I'm not telling you the price to brag, but to make a point. I'm tempted to use them, but horror stories that show up online have steered me away so far.

2 Pirelli tubes on the left

Except for my inner tubes. Previously I used the very expensive Pirelli TPU inner tubes for my bike. I am now using TPU inner tubes made from China. They are so many different brands now. China has created many cheaper alternatives to the popular TPU-based inner tubes from Pirelli or Tubolito that cost $30 compared to $8 ones from China. Well, far so good, they have not let me down yet.

What do you readers think? Are Chinese brands taking the world by storm? BYD cars are now most popular in Singapore while mainland Chinese food and beverage brands are also growing their brands here.