Salt (sodium) causes the body to retain water, which increases the volume of blood and the pressure in your arteries. Most people eat far more than recommended, largely from processed and restaurant foods rather than the salt shaker. Some people are more 'salt-sensitive' than others, including older adults and some ethnic groups, but reducing salt benefits blood pressure broadly.
Health bodies generally advise no more than around 5 to 6 grams of salt (about one teaspoon) a day for adults. Reading labels, cooking from scratch, and using herbs and spices instead of salt all help.
Salt substitutes can help but some are high in potassium, which is unsafe for people with kidney problems or on certain blood pressure medicines, so check with a doctor or pharmacist first. If you have high blood pressure, combine salt reduction with other lifestyle steps and any prescribed treatment.