Never Mind the Bullocks, Here's the Science (7 page)

We partially understand the link to cystic fibrosis. In cholera, the bacterium
Vibrio cholerae
makes proteins that interfere with the movement of chloride and sodium ions, so that a huge surplus of these ions remain in the gut. These ions have an osmotic action, and drag water from the bloodstream into the gut. From there, the easy way out is down to the anus and so the rice water stools gush forth.

In the disease cystic fibrosis, there is a defect in the transport of ions across cell membranes. This defect lessens the harmful effect of the cholera bacterium.

Oral Rehydration Therapy—Theory

If only there were a way to ‘trick’ the cholera-infected gut into absorbing water.

It turned out that there was—and it depended on a scientific discovery.

Only as recently as the 1950s did Western physiologists realise that there are two quite separate mechanisms for absorbing water from the gut into the bloodstream—a Passive Mechanism as well as an Active Mechanism.

In the Passive Mechanism, the water simply diffuses down a concentration gradient—or a ‘gravity gradient’ if you want to be technical—in the same way that a ball rolls down a hill. This Passive Mechanism doesn’t work in cholera victims, because the cells lining their small intestine are poisoned.

The Active Mechanism can shift 10 to 100 times more water than the passive one. It needs both glucose and sodium to work,
and uses these chemicals to drag water out of the gut into your body. (It can work with fructose instead of glucose, but it will just run more slowly.)

How Much Sugar?

To allow the Active Mechanism to carry water across the gut wall into the bloodstream, the level of glucose in the water needs to be around 3%. The Active Mechanism will not work any faster at higher concentrations.

But some of the so-called sports drinks have glucose levels as high as 9%. This is to provide fuel for muscle and brain (typically 30-80 g/hr). But a level this high can actually lead to a loss of electrolytes and slow the absorption of water.

It can also possibly increase the risk of tooth erosion. Increased tooth erosion occurs when you drink small quantities frequently. The sugars remain in the mouth for a while, becoming a food supply for bacteria. The mouth needs time to restore its balance after each drink. If you have one small drink, and then another small drink, the mouth does not get a chance to restore itself. Unfortunately, this is how sports drinks are commonly drunk. So athletes are often advised to squirt the drinks towards the back of the throat, rinsing with water afterwards, both during and after their exercise sessions, in order to take good care of their teeth.

The Position Paper of the American College of Sports Medicine recommends that sports drinks have 4-8% sugars, with 6-7% being optimal.

This provides the best compromise between intestinal absorption and fuel supply, i.e. between fluid and fuel.

ORT—Practical Theory

By the 1960s, this knowledge led to the first modern use of Oral Rehydration Therapy (ORT). ORT is just a fancy name for carefully measured salts and sugars dissolved in germ-free water. In the early 1960s, Dr Robert A. Phillips used ORT to treat patients with cholera. But this did not attract the attention it deserved in medical circles.

One of the first major (and widely recognised) uses of ORT happened as a result of the Indo-Pakistan War in 1971. Wars always affect civilians, and nine million refugees had poured into India from Pakistan. One refugee camp alone held one-third of a million refugees. Overcrowding led to poor hygiene and, ultimately, cholera. Intravenous (IV) therapy for the cholera worked, but was so expensive that only very few patients could be treated using this method. In the refugee camps where IV therapy was being used, the death rate for cholera victims was still 25%. It was so high because most of the patients who needed IV therapy actually did not get it, simply because the medical staff had run out of costly IV sets and the costly sterile fluids.

Something had to be done. Dr Dilip Mahalanabis knew that Dr Phillips had previously used ORT successfully. He and other doctors took over the Johns Hopkins Medical Library in Calcutta (now Kolkata), set up assembly lines to weigh out the ingredients in the correct proportions, poured them into plastic bags, and sealed them with a hot iron. They then used non-medical volunteers (the friends and relatives of the patients) to add the salts to clean water and administer the salty liquid orally to the patients.

ORT Solution

There are several variants of Oral Rehydration Therapy (ORT) solution. A typical commercial 1 litre preparation would contain:

• 2.6 g of sodium choloride (NaCI, to replace lost sodium)
  
• 2.9 g of trisodium citrate dihydrate (Na
  ₃
  C
  ₆
  H
  ₅
  O
  ₇
  .2H
  ₂
  O, to correct the acidosis that comes with diarrhoea, and to help the absorption of sodium)
  
• 1.5 g of potassium chloride (KCI, to replace lost potassium)
  
• 13.5 g of anhydrous glucose (C
  ₆
  H
  ₁₂
  O
  ₆
  , to help the water cross from the gut into the bloodstream).
  

If a commercial solution or an ORT sachet is not available, you can get by with adding to 1 litre of water:

• 8 level teaspoons of common sugar
  
• 1 level teaspoon of table salt.
  

You can also add half a cup of orange juice or mashed banana for its potassium content.

Sports drinks are not a substitute for ORT for clinically dehydrated people – although they would be better than plain water.

First, they contain too much sugar. Their higher sugar level (around 6%) is fine for refuelling, but it also slightly delays transfer of water from the gut into the bloodstream. (The so-called energy drinks can carry more than 8% sugars, which can delay gastric emptying.) Second, they have too few electrolytes. If their electrolyte level were high enough to act as an ORT drink, they would taste too salty.

ORT—Practice

When ORT was used, the death rate in cholera victims dropped from 25% to 3%. This occurred because the treatment worked in most cases, and it was cheap enough to treat most of the patients.

In 1978,
The Lancet
wrote that ORT is ‘potentially the most important medical discovery of the 20th century’.

Worldwide, the average child under the age of five has 2.2 episodes of diarrhoea each year. In 1980, the number of children under the age of five dying each year from diarrhoea was 4.6 million. By 2000, the widespread use of ORT had reduced this to 1.8 million per year. Today, approximately 500 million ORT sachets are made each year—one for every 13 people on the planet.

In the field (away from a hospital), a sachet of various carbohydrates and salts—and sometimes proteins—is added to 200 ml of clean drinking water and simply drunk by the sick person. Oral Rehydration Therapy can be used to treat previously fatal dehydration—and is a far cheaper, and more easily deliverable, treatment than intravenous fluids.

ORT does not reduce the diarrhoea. The diarrhoea continues as before, or even at a greater rate, because the patient is not getting dehydrated—and still has water in the body that can generate rice water stools.

But at least the patient does not die from dehydration.

Childhood Killers

What are the major causes, worldwide, of death in childhood?

In one survey of health professionals, 40% named the major childhood killers as AIDS, tuberculosis and malaria.

However, in reality, the three major killers of children are pneumonia, diarrhoea and malaria.

Birth of Sports Drinks

The medical research into ORT led to the development of the now popular ‘sports drinks’. One of the very first commercially available sports drinks was Gatorade. It was, like ORT, a combination of carbohydrates (sucrose, glucose and fructose) and electrolytes (sodium and potassium), with added lemon or lime (to improve the flavour).

However, the composition was different from ORT. It had a higher carbohydrate content (because it was designed to refuel both muscle and brain as well as enhance intestinal fluid absorption). And it had a lower sodium concentration (to make it more palatable).

It was formulated in 1965 by Dr R. Cade at the University of Florida, to support the Florida Gators Football Team, who, at that time, were on a losing streak. American Football games last for hours, and in the hot and humid climate the players sweated massively and suffered from mild dehydration. The energising and rehydrating effects of the sugars and salts in the Gatorade did help the Florida Gators in the crucial second half of their games. In 1967, for the first time, the Gators won the coveted Orange Bowl.

The Kansas City Chiefs, from Missouri, also had problems with their players flagging in the second half. They too tried Gatorade, which was credited with helping them achieve impressive victories.

Use of Sports Drinks

Some 40 years later, sports drinks are big business. In fact, Gatorade has—after a few legal battles—earned over $80 million for the University of Florida.

By the way, in the bottled drink trade, the sugars and salts are known as ‘pixie dust’ or ‘fairy dust’.

Sports scientists all agree that a little pixie dust does help water absorption. It also helps to maintain your ‘Thirst Drive’. The salts make you feel thirsty, and/or the flavouring makes it more delicious—either way, you drink more.

They also agree that highly trained athletes who sweat a lot each day, thanks to several hours of hard exercise in a hot environment, need sugars to provide fuel for the muscles and brain, and electrolytes and water to replace the losses from heavy sweating. Indeed, many athletes struggle to consume sufficient carbohydrates to meet their daily needs. These athletes would include marathon runners, large football players and tennis players who train for long hours.

But do the rest of us need sports drinks?

To answer that question, you need to realise that the goal of drinking during exercise is to replace the water lost from sweating (and other water losses, such as from urination).

Sweat 101

When you don’t exercise, your kidneys manufacture urine at 20-1,000 ml/hr. But during exercise, the kidneys decrease their rate of manufacture of urine.

How much you sweat is very variable. It depends on environmental conditions—wind and sun exposure, temperature, humidity, sky and ground radiation, etc. It also depends on local conditions—your metabolic rate, your metabolic efficiency (how much work you produce for a given effort), your body weight, your clothing, how hard you work, your history of heat acclimatisation, etc.

Sweating is the major pathway for removing heat during vigorous exercise in warm to hot weather. (Actually, it’s the evaporation that removes the heat, but you have to sweat a liquid
onto your skin before you can evaporate it away.) People working hard can generate 1,000 watts. If their metabolic efficiency is 20%, then they have to get rid of 800 watts continuously, which requires the generation of about 1.2 litres of sweat.

Sweat contains both water and salts. The salts include 5 milliequivalents per litre (mEq/litre) of potassium (range 3-15), 1 mEq/litre of calcium (range 0.3-2), 0.8 mEq/litre of magnesium (range 0.2-1.5) and 30 mEq/litre of chloride (range 5-60).

The effect of sweating is to remove water from the body, i.e. to reduce your Total Body Water (TBW). Your TBW ranges between 45% and 75% of Total Body Mass, the average being 60%. Your TBW is generally regulated to within +/- 0.2-0.5% of Total Body Mass. However, during the post-ovulation phase of the menstrual cycle, women can increase their Total Body Mass by up to 2 kg (due to increased water retention).

But with exercise in hot conditions, a sudden drop of 2% in TBW degrades aerobic and mental performance to an easily detectable level. This 2% drop is a strong warning signal that the athlete is entering a potentially dangerous zone.

Warning – Numbers Ahead!

800 watts = 0.8 kW = 0.8 kJ/sec = 48 kJ/min = 11.46 kcal/min.

Assume that this heat energy is dissipated by evaporating sweat (which is close to 100% water).

The Latent Heat of Evaporation of water = 2.43 kJ/g = 0.58 kcal/g.

So a sweating person who generates 800 watts of waste heat needs to evaporate about 20 g of water/sweat each minute. This works out to about 1,200 g/hr, or 1.2 litres per hour.

Sports and Stress

The effect that different sports have upon the body ranges from relatively non-stressful (such as lawn bowls or billiards) to very stressful (such as marathon running).

How stressful? Consider a person with a fever so excessively high that it is almost lethal. Their metabolism can increase by 100% above normal. But medium-distance runners can increase their metabolism by 2,000% above normal—and survive. Some sports, if continued for too long, can be lethal if they interfere too much with your electrolyte levels, or cause hyperthermia (extremely high body temperature).

What You Need

You need sugar if you burn lots of energy and electrolytes if you have lost some via sweating. This is because sweat removes mainly sodium from your body.