London - Your saliva is possibly not something you have given much thought to — but it plays a vital role in maintaining good health, says Gordon Proctor, a professor in salivary biology at King’s College, London.
“Saliva is a remarkable substance. It might be 99 percent water, but it is far more than that,” says Proctor, a professor in salivary biology at King’s College, London.
In fact, saliva carries the same bacteria found in your gut, as well as powerful substances that fight germs and promote wound healing — which might be why we instinctively pop our finger in our mouth if we cut or graze it.
Now, it is being used to detect serious disease. The University of California, Los Angeles recently announced that it had developed a £15 (about R300) saliva test to spot early-stage lung cancer before it can be detected with a blood test.
The test looks for fragments of tumour DNA in a single drop of saliva, and can give a result in less than ten minutes.
Saliva is already used to see if someone has had an infection such as human papilloma virus (linked to cervical cancer), and scientists are developing ways of using it to monitor such conditions as diabetes, which would be cheaper and easier than urine or blood tests.
Here, we look at the sometimes surprising significance of saliva...
Your spit contains testosterone
Men and women’s saliva contains hormones including testosterone, oestrogen and progesterone, cortisone and melatonin.
“Hormones such as testosterone and oestrogen are fat-soluble, so easily pass through cells walls into the salivary glands,” says Professor Proctor.
It also contains calcium, antibacterial compounds and human cells shed from the mouth lining, which is why a swab saliva test can analyse DNA.
“Without it, you would be prone to nasty infections such as oral thrush, ulcers and gum disease,” says Professor Proctor.
You make different types of saliva
Saliva is produced by the salivary glands. There are three pairs of them: in the cheeks (the parotid glands), the jaw (submandibular) and under the tongue (sublingual), which send saliva through ducts into the mouth. Each produces a slightly different formula.
“The parotid glands produce watery saliva, which helps moisten food when you chew,” says Professor Proctor.
Saliva from under the tongue is much stickier and is the special “protective layer” that coats the inside of the mouth when you are not eating.
We produce less saliva at night because we’re effectively fasting, so there’s no chewing action to stimulate the flow —that’s why we can wake up wanting water.
When we see and smell food, the brain signals the salivary glands to produce more saliva. “Even more is produced when we start chewing,” says Professor Proctor.
This is because mechanoreceptors (sense cells that register touch or sound) in the lining of the mouth and in the gums register the pressure of chewing and pass signals to the brain.
Teeth would rot without it
Saliva is also vital in helping to prevent tooth decay and erosion. “Saliva contains a buffer that neutralises acidity,” explains Dr Mervyn Druian, a London-based dentist.
There are also potent antibacterial compounds in saliva, which help to eliminate plaque-causing bacteria.
Most importantly, the constant flow of saliva washes away excess bacteria, so they cannot get a foothold.
Saliva even helps to harden teeth because it contains calcium, which is absorbed into the dentine, the pulpy layer beneath the enamel.
Dry mouth? You could be ill
The average person produces between one and two litres of saliva each day, around the same as your urine output.
Lack of saliva may be a sign of a health problem.
Sjogren’s Syndrome, an autoimmune disorder, causes gradual damage to the salivary glands, which can cease production altogether.
“This is not life-threatening, but it can damage quality of life,” says Professor Proctor.
It affects nine times as many women as men and tends to strike in middle-age. People who have undergone radiation treatment or chemotherapy may produce lower levels of saliva, or none at all.
“Radiation treatment for head and neck cancers can damage salivary glands,” says Dr Guy Carpenter, an oral biologist at King’s College London Dental Institute.
Sometimes, the glands heal, but some patients may be left permanently affected.
Lack of saliva is also linked to the menopause — falling oestrogen levels can, in turn, reduce moisture in mouth and nose mucus membranes.
It can predict your health
A study published last December in the journal PLOS One, a peer-reviewed scientific journal published by the Public Library of Science, found that levels of a particular antibody found in saliva falls as death approaches.
Researchers at the University of Birmingham measured levels of an antibody known as A (IgA) in 639 adults and tracked them for 19 years.
The antibody is secreted by white blood cells, which fight infection in the body.
Dr Anna Phillips, a health psychologist at the University of Birmingham, who led the research, explained: “How saliva could be used in check-ups remains to be seen.
“We need to better understand what secretion rate of the antibody would be considered cause for concern, but we could certainly say that it would be a useful early indicator of risk of dying.”
Daily Mail