Lactose intolerance is a condition the vast majority of the world's population suffer from to some degree, particularly adults. What's more is, whilst lactose intolerance is so common, and some people may suffer terribly with it, the majority of sufferers do not know they are lactose intolerant, and are unaware it is lactose which is causing their bodies distress.

So what is lactose, and why are so many people intolerant to it?

Lactose is one of the prime sugar compounds found in milk. It is present in any milk which comes from animals or humans. In our bodies, we have many different kinds of enzymes which deal with our food intake. These enzymes are basically converters. They take the raw materials we consume, and convert them into special fuel and nutrients our bodies can then use. Without these enzymes, our bodies wouldn't be able to run on what we give them as raw materials, almost like a diesel car wouldn't run if you put petrol into it.

So these enzymes are critical to our survival and wellbeing. The enzyme which is responsible for converting lactose into something useful is lactase, which is produced within the small intestine, and the something useful is glucose. Glucose is our bodies' main energy source, and our brains and nervous systems rely only on glucose to function, so it is vitally important.

As babies, our lactose tolerance tends to be at its highest in our lifetimes. This is because of human evolution, where females produce breast milk and babies are weaned on this milk, and sometimes only on this milk, for a short time. Because a baby needs glucose, and milk may be the only thing consumed in the earliest days, these high levels of lactase production ensure the baby gets the most from their feed, wasting very little lactose.

When a baby gets older, between the ages of 2 - 5, we tend to lose much of our tolerance to lactose. The reason for this is, although lactose can sustain a baby during the earliest times, it is absolutely inadequate and inefficient as a main glucose source for people who are older and more active. When we get older and begin eating other foods, our main source of glucose is carbohydrates. Because of this, our small intestines begin to produce less of the lactase enzyme, because high amounts simply aren't needed anymore.

The result is, when we drink milk or consume other products which are high in lactose content, our bodies can have a hard time processing all of the lactose due to such low lactase production. This can lead to symptoms such as stomach cramps, nausea and diarrhoea. Of course, symptoms will depend entirely on an individual's lactase production levels and lactose consumption levels.

Although you may not know it, the simple fact is, humans were never meant to continue consuming the quantities of milk we do - if at all - past the weaning period. We have only recently begun to do so since humans domesticated animals such as cows and begun to consume their milk. On the evolutionary scale, the time we've been practicing this is minute, therefore our bodies haven't for the most part genetically evolved to continue producing good levels of lactase in adulthood. This isn't the case for some people, however. In parts of northern Europe where dairy farming and milk consumption have been going on for generations and generations, some people have genetically developed what is known as 'lactase persistence' into adulthood, where lactase production has remained high allowing high quantities of milk to be consumed without any side effects. Northern Europe and those of Northern European descent are thought to be the most lactose tolerant people in the world.

It is worth noting not all babies are lactose tolerant, and some may suffer side effects. If you think your baby may be lactose intolerant, you should raise your concerns with your doctor immediately to prevent the baby from suffering.