Author of Keep Healthy After Cancer, leading oncologist Professor Robert Thomas examines the rarely discussed negative effects of cycling on male health – and how diet can help…

Whether you’re commuting, being a weekend-warrior in a gruelling sportif or just having fun with the kids, cycling is an excellent way to increase physical activity. Middle-aged men in Lycra, in particular, spend millions on bikes and gadgets, but is life on two wheels actually damaging their health?

The biggest risk factor, of course, is being knocked off your bike. Accidents aside, however, there are other, rarely discussed, potential health issues for men.

Too much time in the saddle can cause both cellular damage and direct trauma to the perineum (the area from the anus to the scrotum) leading to increased incidences of erectile dysfunction, waterworks problems, osteoporosis and even infertility and prostate cancer. 

How big is the actual risk of these conditions for riders though? And does the risk supersede the obvious positive health benefits of exercise?

We know that regular exercise lowers the risk of multiple chronic diseases including heart disease, stroke, dementia, obesity, diabetes and cancer itself [Thomas].

A recent review in the British Journal of Sports Medicine highlights the biochemical changes which happen after exercise, including reducing inflammation, improving immunity and insulin sensitivity [Thomas].

Another study reports that exercise improves skin tone, mental activity and slows our biological clocks embedded in our DNA (telomere length) [Ornish]. 

And there’s anecdotal evidence in reams; many cyclists argue they are likely to be more radiant, intelligent, virulent and biologically younger than their sedentary counterparts. 

CYCLING AND PROSTATE CANCER 

An increased risk of prostate cancer has been reported amongst cyclists but the evidence remains weak.

The largest study, involving 5,000 men who cycled regularly, reported a six-fold increase in prostate cancer incidences among those who trained more than eight hours weekly, compared to men who trained less than 3.75 hours [Hollingworth].

What was less widely highlighted in the media was that all men in the study had a cancer rate three times times less than the general population, because there is less prostate cancer in cyclists compared to sedentary men.

Nevertheless, the increased risk in elite athletes compared to other cyclists is probably genuine, so it is worth considering some practical nutritional strategies which can: mitigate the potential risks, ameliorate the overall benefits of cycling and at the same time, enhance sports performance. Here’s how you can do it:

ENERGY PRODUCTION AND OXIDATIVE STRESS

A vast amount of energy is required to fuel the muscles during intensive and prolonged aerobic regimens. It’s important to keep levels of sugar in the blood stream as constant as possible during exercise.

Processed sugar is therefore not an ideal source of energy as this creates peaks of blood sugar levels leading to excess insulin and then hypoglycaemia

Complex carbohydrates are better, as they slowly broken down to glucose and fats which are broken down to glycerol and fatty acids. All these feed into the three biochemical pathways of the energy production pathways, namely; glycolysis, the Kreb’s cycle and oxidative phosphorylation (OXPHOS).

As cycling is an aerobic sport, for the majority of the time the tissues are well oxygenated for the majority of the time, so OXPHOS, which requires oxygen to convert food into ATP fuel packets, is the preferred and most efficient pathway.

A by-product of OXPHOS, however, is the formation of reactive oxidative species (ROS) that which can damage DNA and other cellular structures.

A state of high-levels of ROS is known as ‘oxidative stress’ and if this occurs in the chondritic cells of the joints, it leads to arthritis and poor recovery in muscle cells. In all cells, it can lead to premature ageing and genetic mutations, which are known to cause cancer. In order to minimise oxidative stress, it’s necessary to consider two fundamental issues. 

1. Supporting antioxidant enzymes

The building blocks for the antioxidant enzymes, include essential minerals, vitamins and polyphenols. Deficiencies in essential nutrients should be avoided, particularly with zinc, copper and selenium which are required for one of the main enzymes, superoxide dismutase.

That said, studies have also shown that over-correcting levels of minerals and vitamins do not confer additional advantages. Of more concern, excess vitamin A, or Vitamin E and selenium could actually increase the prostate cancer risk [Klein].

Putting these nutrients into a supplement is therefore not recommended unless the individual has had a micro-nutrient blood test (see cancernet.co.uk) revealing a specific deficiency which requires correction.

Otherwise, the best way to avoid deficiencies is with a varied diet rich in seafood including oysters, clams and fish as well as nuts and leafy greens vegetables. 

Likewise, cyclists should boost their diet with polyphenol-rich foods, which promote antioxidant enzyme production, such as dark green vegetables, spices, herbs, teas, berries, nuts, colourful vegetables and fruits [Thomas].

The World Cancer Research Fund reported that individuals who eat these foods have a lower risk of cancer and well-conducted trials of polyphenol- rich whole food supplements have demonstrated significant benefits.

The largest, and most notable of these, was the UK government-backed national Pomi-T trial which showed that a supplement containing a blend of purified, high grade turmeric, pomegranate, green tea and broccoli prevented early prostate cancer progressing to more advanced disease compared to men taking a placebo [Thomas].

Whole food supplements, such as this, are a logical choice for cyclists, as part of a balanced diet, as since higher levels of polyphenol not only potentially reduce the damage from free radicals generated by energy production; their anti-inflammatory effects may counterbalance the repeated trauma from the saddle.

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Furthermore, polyphenols are essential for tissue repair, including helping to maintain joint health. Finally, the nitrates in these foods are also beneficial for cyclists as they are converted to nitric oxide. This relaxes smooth muscles around arteries enhancing blood to tissues, which improves oxygenation, muscle and heart recovery, erectile function, cognitive function and lowering blood pressure. 

2. Avoiding carcinogens and pro-inflammatory toxins

In addition to unaccustomed or strenuous exercise factors that increase oxidative stress,  these include excess chronic inflammation caused by obesity, processed sugar intake, acrylamides formed by super heating carbohydrates (crisps and even some cereal and energy bars); and Polycyclic Aromatic Hydrocarbons and Heterocyclic Amines found in processed and burnt meats.

THE EFFECTS OF CYCLING ON TESTOSTERONE, FERTILITY AND ERECTILE FUNCTION

Although regular exercise delays the natural age-related decline in testosterone, strenuous exercise accelerates this drift. This is because after intense exercise, testosterone increases for about an hour (depending on the level of fitness and age).

However, in response, the body then adapts by signalling the testes to reduce production [kraemer]. A fall in testosterone levelsin the long-term can contribute to fatigue, poor motivation, reduced erythropoietin levels, leading to anaemia, low libido and erectile dysfunction (ED). In addition, pressure to the perineum can damage the adjacent nerves and blood vessels supplying the penis, which can worsen ED.

An actual increase in the erectile dysfunction rate is, however, debatable with some arguing that cyclists are more motivated by thoughts of their next ride rather than their “next ride”, if you’ll excuse the pun.

Some studies, such as the large UK cyclist survey, report no problems with ED but others, such as the Boston cohort study, found that ED was three times more likely especially among cyclists who use saddles causing penile numbness.

In women, repeated friction can lead to vaginitis, soreness, bacterial and yeast infections. In terms of infertility, the combination of ROS and lower testosterone explains the increased number of abnormal sperms and lower viable sperm counts among elite cyclists, although an effect on actual fertility has not been established [Leibovitch].  

HOW TO KEEP TESTOSTERONE LEVELS RIDING HIGH

Low levels of vitamin D, zinc, magnesium, selenium and chromium are associated with a lower levels of testosterone [Prasad]. Reassuringly, the same studies showed that correcting these deficiencies increased normalised testosterone and can also improve muscle strength [Cinar, Grimaldi].  

Cholesterol is a precursor in the testosterone biosynthesis pathway, so increased healthy fat intake is advised, preferably from plant sources such as coconut, avocado and olive oil as well as smaller oily fish such as mackerel, sardines and anchovies. Avoid statins unless you have other risk factors for cardiac disease as these lower testosterone [Wang].

Eat less processed sugar and fewer refined carbohydrates as these increase blood sugar and risk type two diabetes, which is linked to lower testosterone. Consider carbohydrates which have higher protein content, such as wild rice and quinoa.

THE RISK OF OSTEOPOROSIS

Lower testosterone combined with a general lower body mass index of cyclists and lack of weight-bearing baring when exercising can lead to significant loss of calcium in the bones (osteoporosis) [Nagle].

So severe was professional cyclist Chris Boardman’s osteoporosis that he was forced to retire at the age of 32. Adopting the measures to maintain testosterone are important, namely  particularly Vitamin D supplementation in the winter and sensible sun exposure (avoiding sun burn) at other times [Nemptsch].

It would be sensible to introduce a weight-bearing baring exercise into training regimens, such as jogging or squatting with weights.

It’s protein from plants, rather than meats, which are best for bone health, so increased intake of whole soy, chickpeas, lentils and beans is encouraged [Beasley]. A very large recent study also reported associated higher intake of green tea with better bone health [Thomas]. 

In conclusion, the biochemical changes which arise after exercise have significant anti-cancer and chronic disease protection properties.

Nevertheless, the generation of free radicals, a fall in testosterone and local inflammation remain potential concerns for those undertaking intense cycling.

Some simple dietary changes can help to maintain testosterone levels and bone density, and adopting a healthy polyphenol-rich diet would be very sensible practice. 

Professor Robert Thomas is a consultant oncologist at Bedford and Addenbrooke’s Cambridge University Hospitals and Professor of Biological and Exercise Science at the University of Bedfordshire. He’s also author of Keep Healthy After Cancer.

References:

• Hollingworth M (2014). Erectile dysfunction & prostate cancer in cyclists: J Men Health;11:75-9.
• Leibovitch I (2005). The vicious cycling related urogenital disorders. Eur Urol; 47:277-87. 
• Thomas R (2017). The biochemistry of exercise. BJSM 2017;51:640-644.
• Thomas R (2015).  Phytochemicals in cancer prevention and management. BJMP; 8 (2)
• Thomas R (2014). The UK National Pomi-T study. Prostate Cancer & Diseases 7, 180-6 
• Kraemer W. Hormonal responses and adaptions to exercise Sports Med. 2005;35(4)339-61.
• Nagle K. systemic review of bone Health in Cyclists. Sports Health. 2011; 3(3): 235–43.
• Ornish D (2013). Effect of comprehensive lifestyle changes on telomerase activity and telomere length. The Lancet oncology;14(11):1112-1120. 
• Nimptsch (2012). Association between plasma 25-OH vitamin D and testosterone levels in men. Clinical Endocrinology, 2012 77(1), 106-12 
• Wang C. (2005). Low-Fat High-Fiber Diet Decreased Serum and Urine Androgens in Men. Journal of Clinical Endocrinology & Metabolism, 90(6), 3550-3559.
• Grimaldi A (2013). 25(OH) Vitamin D Is Associated with Greater Muscle Strength in Healthy Men and Women. Medicine & Science in Sports & Exercise, 45(1), 157-162.
• Prasad, A. (1996). Zinc status and serum testosterone levels in adults. Nutrition, 12(5), 344-348.
• Cinar V. (2010). Effects of Magnesium on Testosterone Levels of Athletes and Sedentary Subjects at Rest and after Exhaustion. Biological Trace Element Research, 140(1), 18-23.
• Kraemer W (2013). The effects of soy and whey protein supplementation on acute hormonal reponsesresponses to resistance exercise in men. Journal of the Am Col Nutrition, 32(1), 66-74.