Salt: the risks
The taste buds of our tongues and mouths are receptive to five basic tastes that form the building blocks of flavour: sweet, sour, bitter, umami (pleasant savoury taste) and salty. 
As well as making food appealing salt is necessary for the body’s successful functioning. It promotes secretion of the healthy stomach acids that kill pathogens like bacteria, fungi and yeast, and also plays a part in the body’s water-regulation system. Together with potassium, the salt we eat helps control the flow of water through every cell of our bodies; with our kidneys maintaining a careful balance and eliminating any salt we do not need. Even the proper functioning of the brain can be affected by eating too much or too little salt. 
However, consuming excessive salt poses serious health risks. When the level of sodium rises, the kidneys can struggle to keep up and so the body holds onto water to dilute the accumulated salt. This increase in the fluid surrounding our cells and the volume of blood in the bloodstream raises blood pressure and also puts a strain on the delicate blood vessels leading to the kidneys. Over time this can lead to permanent damage, known as kidney disease, with the kidneys becoming increasingly less able to filter out the toxic and waste products, which build up, causing slow poisoning.  The strain on our arteries caused by the increased blood pressure causes arterial walls to thicken, raising blood pressure still further.
The heart, in response, is forced to pump harder – a job that becomes more and more difficult over time, as the walls of the aortic valve harden and narrow (stenosis) in response.  Mild narrowing may not cause symptoms, but if this grows more severe it may lead to dizziness, chest pains and irregular heartbeat, along with risks of heart failure, hypertension or stroke. Excessive sodium can also contribute to osteoporosis, ulcers and stomach cancer. 
Given these dangers, and because we tend to crave more salt than the body needs, it is important to be aware of how much salt we eat.
It is easy to be consuming more than we might realise: around 75% of the salt we consume is already present in foods like cheese, processed meat products, crisps, ready meals, bread and sauces – and in less expected places, such as breakfast cereals, ketchup and stock-cubes.  The UK average is 8.1g (one and a half teaspoons) – but to reduce risk of disease adults should be eating no more than 6g (2.4g sodium) of salt each day.
The levels for children and babies are much lower: less than 1g daily for babies, 2g (0.8g sodium) for infants aged 1-3, 3g salt (1.2g sodium) for children aged 4-6 and 5g salt (2g sodium) for children aged 7-10. Children over 11 can eat the same levels of salt as an adult (6g). 
So what can we do to protect ourselves, other than cutting back on the salt we use in our cooking – and removing the salt shaker from the dinner table?
Firstly, there are low-sodium substitutes available in supermarkets and health-food shops which replace sodium with potassium as the key ingredient. It is important to discuss using these with your doctor before making the switch, however, as while they reduce dietary salt they can be harmful in combination with certain medications or where there is a risk of kidney disease. 
Secondly, become salt-aware. Get to know your way around nutrition labels and swap to lower-sodium alternatives. Choose reduced-salt, unsmoked bacon and salt-free tinned veg (if you cannot find salt-free canned tuna, pulses or vegetables, rinse them under cold water before using them). Switch your crisps and salted nuts for low-salt or unsalted versions, or consider substitutes like carrot sticks and celery. Change to fresh meat or fish rather than processed or pre-packaged meals. And when cooking, rather than using salt, add more flavour by using black pepper, herbs and spices; or adding garlic, ginger, chilli or lime.  The internet is packed with recipes that show that low on salt can still be high on taste – one of our favourites is this low-salt lasagne.
Tsugane, S. and S. Sasazuki, ‘Diet and the risk of gastric cancer: review of epidemiological evidence’, Gastric Cancer, 2007. 10(2): p. 75-83.