Run Well

by Juliet McGrattan

  NHS IBS diet video guide: www.nhs.uk/conditions/irritable-bowel-syndrome-ibs/ibs-diet-video-guide/

  Drinkaware: www.drinkaware.co.uk

  Macmillan Cancer Support www.macmillan.org.uk

  Chapter 5

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  The Urinary System

  As runners, we’re repeatedly told how important it is for us to stay hydrated, so the urinary system, where water is both retained and lost from the body, is crucial for us. Understanding how that system works and being aware of potential problems will help us to run safely and healthily. So whether it’s a leaky bladder, a troublesome prostate or concerns about kidney damage, this chapter has it covered. Grab a big drink of water and read on!

  The urinary system includes your kidneys, bladder, ureters (tubes from kidney to bladder) and urethra (tube from bladder to the outside). Its main functions are to control the fluid balance of the body and to produce urine to remove toxins.

  Around 150 litres of blood pass through your kidneys each day. Most people have two kidneys but it’s possible to live normally and healthily with just one. You may have heard the kidneys’ role described as ‘cleaning the blood’ and this paints a perfect picture. Kidneys contain about a million nephrons. These are filtering units which sort through the blood, taking out the bad bits and keeping the good. The way they do this is mind-blowingly clever. Blood arrives at the kidneys in the renal artery. The pressure in this artery is pretty high and the blood is pushed forcefully through the first part of the nephron, called the glomerulus. This is a knot of thin-walled blood vessels that act as a sieve. Big molecules such as blood cells and proteins remain in the blood while smaller ones such as urea (a waste product), water and ions like sodium slip through the sieve and into the kidney tubule to form urine. However, not all the small molecules are bad, so the kidney needs to selectively take back the ones it needs. The kidney tubule is long and runs close to the blood vessels so water, glucose and other nutrients can be reabsorbed back into the blood, ensuring only unwanted waste makes it to the urine.

  Kidneys also have an important role in maintaining blood pressure. They detect pressure, fluid and body salt levels and can secrete a substance called renin, which triggers a system called the renin-angiotensin system. If blood pressure is falling then angiotensin will constrict the blood vessels, to increase pressure and also trigger release of a hormone called aldosterone from the adrenal glands, which are located just above each kidney. Aldosterone messages the kidneys to reabsorb more sodium and water from its tubules, which increases the blood volume and restores the balance again. If blood pressure is too high then the blood vessels are dilated and the kidneys take back less sodium and water to reduce the blood volume and pressure.

  The ureters transport urine from the kidneys to the bladder where it’s stored until you want to have a wee. The bladder is actually a muscular bag which can expand and then shrink back down again. It can hold about 500mls of urine and when it’s getting stretched, it sends messages to your brain that it would be a good idea to find a toilet. When the time is right, the bladder muscle (called the detrusor muscle) contracts, forcing the urine out. At the same time, the sphincters and pelvic floor muscles, which keep urine in, relax and allow the urine to flow.

  It’s a complex system with many functions which are crucial to us as runners. Let’s look at some questions related to the urinary system to further help us understand how it all works and to make sure we can run healthily.

  Q I know that hydration is important for runners, but how much should I drink when I run?

  A How much fluid you need when running depends on many variables, including your weight, the air temperature, your fitness, how much you sweat, your intensity and duration of exercise, what you’ve eaten… the list goes on and on. If you want to get very technical about it then you can follow the steps below to see how much fluid you’ve lost during a run. You do need to remember that there will be day-to-day variation so you can’t assume this amount is what you need every time. It’s just a guide. The simple answer is to just be directed by your thirst. You may have heard of the concept that if you’re thirsty you’re already dehydrated, but your thirst mechanism is well-designed and very sensitive. It will let you know when taking on water would be a good idea and it will tell you well ahead of time. You just need to tune into it. If you’ve had a drink before you exercise then you might not need one at all during activity unless it’s a very hot day, your effort level is intense or you’re running for over an hour. There are plenty of experienced runners doing ten-mile weekend runs without drinking while they’re on the move. We can sometimes get too hung up on the whole water issue. It’s sensible to take water with you on longer runs and drink to thirst. What you drink is important too, because replacing fluids lost through running means replacing salts as well as water.

  Did you know?

  Sweating is our body’s way of cooling us down. Heat is lost when sweat evaporates from our skin. We have millions of sweat glands in our skin with more in areas such as our armpits, forehead and palms. Sweat contains mostly water, but also lactic acid and urea. Minerals such as sodium, potassium, calcium and magnesium are lost in sweat, as are tiny amounts of trace metals such as iron, copper and zinc.

  Q What is hyponatraemia and how can I avoid it?

  A Hyponatraemia means low blood sodium levels. Sodium is a mineral which the body’s nerves and muscles need to function properly, but it also plays a crucial role in fluid balance in the body. Have you heard of osmosis, the process by which water is drawn across a membrane from a less concentrated solution to a more concentrated one? The kidney uses sodium to enable osmosis. Ions such as sodium are initially filtered out of the blood by the kidney, and into the tubule, to make urine. The kidney then selectively reabsorbs sodium back into the blood. By doing this it increases the concentration of sodium in the blood and water is then drawn in too. By moving sodium and regulating blood concentration, the kidney can move water back into the system to maintain fluid balance and blood pressure. If you ingest excess salt, then high sodium levels can mean that more water is drawn into your bloodstream and high blood pressure can result.

  Sweat contains large amounts of sodium, so over a run of marathon distance or longer, you can lose significant amounts. At the same time, ingesting large quantities of water will literally dilute your blood. The result can be hyponatraemia – potentially dangerous low sodium levels, where cells begin to swell with water and malfunction. Hyponatraemia can present as weakness, confusion, cramps, nausea, headaches and, in severe cases, seizures and even death. This is why long-distance runners need to pay attention to their hydration and not drink large quantities of water at every drink station. Drinking to thirst is better and also making sure that some of what is consumed contains electrolytes (minerals), which include sodium. You can use specifically designed sports rehydration drinks or you can make your own using fruit squash and a pinch of salt. Sodium can also be replaced through eating salty foods such as pretzels or taking salt tablets. The longer and hotter the race, the bigger the risk. Being aware of the potential of hyponatraemia is important, but at the same time don’t limit your fluid intake because you are scared of it, because you’ll be at risk of harmful dehydration instead! Use your common sense, adapt to race conditions and practise your fuelling to minimise your risks.

  TRY THIS

  AT HOME

  Running hydration

  If you’re concerned about your hydration or simply curious about how much fluid you’re losing during a run, then you can try this simple test. This will give you a good idea about how much you sweat, but don’t forget that you lose fluid through your breathing and panting too.

  1 Immediately before you run, weigh yourself naked.

  2 Go for a run (dressed!) – a one-hour run is recommended.

  3 After your run, strip naked again, towel dry off any sweat and weigh yourself.

  4 Subtract your after-run weight from your pre-run
weight and convert this to millilitres, e.g. 70kg-69kg = 1kg and 1kg = 1000mls.

  5 If you have had a drink during your run, then add it to this total, e.g. 1000mls + 250mls = 1250mls.

  6 This total is your fluid loss over the hour of running – 1250mls or 1.25 litres per hour.

  You don’t need to arrive home in perfect fluid balance. This will just give you an idea how much you need to replace after you’ve run and help you decide how much to drink while you’re on the move. Remember, it is only a guide and will vary according to how hot or cold the weather is, how intense your session was and other daily variables. If you need to wee or poo then you’ll have to do it before the pre-run weighing or after the post-run weighing, otherwise you’ll be losing body fluids that haven’t been measured.

  Q Can running a marathon cause kidney damage?

  A Learning about the hard work the kidneys have to do to maintain fluid balance, it may make you wonder whether running marathons, where hydration can be pushed to its limits, could actually harm the kidneys. Previous studies have shown that up to 85 per cent of ultramarathon runners have some degree of temporary kidney damage at the end of a race. But what about marathons? A small study of 22 marathon runners (41 per cent men), in the 2015 Hartford Marathon in the USA, found evidence of kidney damage with 73 per cent of the runners tested immediately after the marathon showing changes that indicated injury to the tubules of the kidney. Further tests taken 24 hours later showed some improvement, but not complete resolution of these changes. A different study of 167 amateur runners, between age 39 and 61, at the Berlin marathon showed that abnormalities in kidney function induced by running all returned to normal within two weeks after a marathon. What we don’t know is what happens beyond that. Could years of repeated acute episodes of stress on the kidneys affect their future function? Or is the opposite true – that these periods of hardship only act to strengthen and maximise the response of the kidney to injury and are in fact protective? We aren’t even sure exactly what it is about marathon running that causes damage to the kidneys. It’s perhaps a lack of blood flow to the kidneys, dehydration, damage from muscle breakdown or a rise in core body temperature – it may well be a combination of all four.

  There are blood tests that are used to check for chronic kidney disease (CKD), which is essentially ‘wear and tear’ on the kidneys, and these are frequently carried out on people with medical conditions such as diabetes and high blood pressure. It would be interesting to know if life-long endurance runners have a higher or lower incidence of CKD, but runners are healthier, less likely to have medical conditions or see the doctor for routine tests, so it would be hard to prove. What we can be sure of is that regular exercise helps to lower our risk of high blood pressure and type 2 diabetes, both important causes of kidney disease. We can look after our kidneys by keeping hydrated, respecting hot weather running and training sensibly. So far there isn’t convincing evidence that running marathons damages your kidneys in the long term.

  Did you know?

  Each kidney measures 10 to 15 centimetres long and weighs around 160 grams which is equivalent to the weight of three tennis balls.

  Q Is it safe to use anti-inflammatories when you run? I’ve heard it can damage the kidneys.

  A Non-Steroidal Anti-Inflammatories (NSAIDs) are a family of drugs which include ibuprofen, diclofenac and naproxen. Ibuprofen can be bought over the counter in the UK and is widely used by runners, because it gives effective relief for musculoskeletal pain. It’s not uncommon for runners to take ibuprofen before a long run in anticipation of pain, particularly when they want to perform well in a race or when they are running with an injury. We know that long-term use of NSAIDs can cause health problems, including kidney damage, high blood pressure, heart attacks and gastrointestinal ulcers, but will a single dose before an endurance run pose any risk? Anecdotally up to 75 per cent of ultramarathon runners take ibuprofen before racing so this population is ideal for identifying any potential harm to kidneys. A study published in 2017 gave either ibuprofen or a placebo to 89 runners, to take every four hours during their 50-mile run. Kidney function was tested immediately on finishing the race and 39 of the 89 runners had signs of acute kidney injury at the end of their race. The risk was 18 per cent higher in those that took ibuprofen. For every five runners who took ibuprofen there was one extra case of kidney damage. From this we can conclude that taking ibuprofen during an endurance race increased the risk of kidney damage in this population.

  NSAIDs reduce the amount of blood flow in the kidneys and inhibit the formation of prostaglandins, which usually cause dilation of the blood vessels and increased filtration rates in the kidney. If we add the negative effect of dehydration too then we can begin to see why taking ibuprofen during endurance runs is not a risk-free option.

  Q The nurse said there was blood in my urine when he did a dip test during a health check. Could this be related to running?

  A A dip stick urine test will detect blood in the urine that is not visible to the naked eye. We call this microscopic haematuria (blood which you can actually see in the urine is called macroscopic haematuria). Microscopic haematuria can happen for a number of reasons, including infection, prostate enlargement and bladder or kidney stones. It can also be due to kidney damage and bladder cancer, so it is an important sign. Sometimes the blood is simply coming from sore or cracked skin near the urethra or from contamination by menstrual blood in women. Strenuous exercise can cause blood to leak into the urine. This can be due to the bladder walls hitting against each other during running and blood coming from the resultant ‘bruise’. If the kidney’s nephron or cleaning function is impaired, it may also be due to red blood cells being pushed through the glomerulus, the knot of blood vessels that acts as a sieve (see here). This reduced nephron function may be as a result of decreased blood flow to the kidney when blood is diverted to skeletal muscles during exercise. It seems to be the intensity of exercise which is important and not just the distance run.

  So, we are left with a conundrum. Exercise-induced microscopic haematuria not due to an underlying sinister cause will resolve and doesn’t need any treatment, but recurrently having blood in your urine requires investigation to rule out treatable and significant medical conditions. You will definitely need to have at least one more urine test to determine the next steps. Your nurse or doctor may suggest you avoid strenuous exercise for 24 hours before this. They will need to take the rest of your medical history and the likelihood of other medical conditions causing the haematuria into account before deciding on the best course of action. If your microscopic haematuria is present on multiple dip stick tests, then you will need to have some investigations to look for the cause before assuming it is exercise-related. If it turns out to be purely exercise-related, then it’s worth discussing with your doctor whether you need to take iron supplements to counteract this silent blood loss (see here).

  Real-life runners

  When I found blood in my urine, I suspected it was either an infection or most likely haematuria from running. However, I decided to get a professional opinion and I am glad I did as it turns out it I actually had prostate cancer. My advice is always seek a medical opinion as you never know what it could be.

  Richard Hayes, runner, LEGO consultant and coffee lover

  Q My friend peed blood after an ultra. Is this normal or should he be worried?

  A Blood might be bright red and have some small clots in it or it might be diluted in the urine, turning it pink in colour. The potential causes are the same as those for microscopic haematuria, but the blood loss is heavier and is usually most pronounced on the first wee after a run. It tends to occur after distances of 10km or more and is usually painless. The same conundrum of when and how much to investigate arises, but ultimately blood in the urine must always be investigated so testing is important.

  It’s also important to know that urine can turn a red colour for reasons other than red blood cells being present. Eating dark red fo
ods such as beetroot can result in red urine which is easily mistaken for blood loss. It can also be due to myoglobinuria – myoglobin is a protein found in skeletal muscle. When muscles are damaged and break down (a process called rhabdomyolysis), myoglobin is released and the kidneys filter it out and excrete it in urine, because high levels can be toxic to the kidneys. Myoglobin turns the urine a red/brown colour, a bit like cola, which can be mistaken for blood. Myoglobinuria and rhabdomyolysis can occur in runners after ultramarathons. It usually resolves with time and adequate fluid intake, but there are situations where this may be dangerous and the risk of kidney failure increases. These include dehydration, extreme heat, taking NSAIDs, and running with or soon after a viral or bacterial infection. If you have cola-coloured urine after an endurance race you should seek an urgent medical assessment.

  Did you know?

  Adults produce about 1.5 litres of urine every 24 hours, but anywhere between 0.5 and 2.5 litres can be normal, depending on your size and how much fluid you’ve drunk.

  Q Why do I leak urine when I run and what can I do about it?

  A Around a third of women report leaking urine when they run so you are not alone. The actual figure may be much higher than that, because women find it embarrassing and don’t tell anyone. This type of leaking is called stress incontinence. Running is basically repetitive jumping – you have two feet off the ground at one time and the impact of returning to the ground causes an increased pressure inside the pelvis. Ordinarily the pelvic floor muscles would be able to cope with this, but if these muscles are weak then they’re unable to support the bladder enough to prevent urine leaking out. Being pregnant and giving birth weakens the pelvic floor, particularly if the baby was big or the delivery difficult. Pelvic floor muscles can also be weakened by the falling oestrogen levels of the menopause – as many as half of women over 50 experience some urinary leaking. Straining with constipation, recurrent coughing and being overweight can all stress and damage the pelvic floor muscles.