Leg cramps can be due to a lack of magnesium - and we are very deficient in that - undoubtedly because of the low salt diets we are encouraged to follow. The fact that people often get cramps at night is probably because the body uses more then as it does its cleansing and healing work and because a lot of people sweat in bed at night. Runners often get cramps because the muscles have used all the available magnesium in the body or it has been sweated out.
http://www.mg12.info/articles/cramps.html (I don't agree with the advice to cut dietary fat - most people already cut too much of that out of their diet, but the other advice seems pretty good. I eat high fat, yet I take both salt and extra magnesium (if you take magnesium it should be taken with an equal amount of calcium to keep the balance right) and don't suffer with cramps any more at all)
But just taking more salt isn't necessarily the key. Most of the salt that is sold now is cheap Table salt which is just sodium choride with a few added chemicals to make it flow easier (like sodium ferro-cyanide!).
What you need to take is Celtic Sea Salt which still retains the full quota of other minerals (including magnesium) and trace elements. They may only make up 2% of the salt's constituent parts, but they are necessary as the body uses them all in different processes. As all the elements that make up the Human body work in harmony, a shortage of any one of them can impact on it.
http://www.tjclarkdirect.com/humanbodyelements.htm This contains a list of the 'known' elements in the Human body but there are undoubtedly considerably more. Whilst the other minerals and trace elements in whole salt are only in miniscule amounts, they are still necessary to help in bodily processes and to support the body's use of the elements we get from our food.
Some people will dismiss that 2% as being of no importance, but because so little is known or understood about what is used where, it is difficult to make a judgement call on it. But whole salt has been highly prized for thousands of years for many reasons - not just because it is a great healer (and the trace elements contribute to that) and it is only comparitively recently that salt has been broken down in to its component parts. Cheap Table salt is what is left after all the valuable minerals and trace elements have been extracted and sold for profit.
Without the other elements the body cannot use the sodium chloride properly, and it will unbalance the body chemistry causing all sorts of problems.
I would suggest trying some Celtic salt first - a maximum of a teaspoonful per day (less if you are getting salt from any other source) and see if that helps. It may take a little while to correct, but you can't lose anything by trying. I buy Danival 'Sel Marin' sea salt from my local health shop at just over £2 for a 1 kilo bag so it isn't expensive. If they haven't got any, an independent retailer should be able to order it in. You should be able to get it online.
Since I have been 'taking the salt', my body has been healing all sorts of things and it hasn't impacted on my BP at all - in fact, it's gone down!