Salt

TL;DR

If you are healthy and have normal blood pressure and kidney function - regardless of your diet - you probably have no need to limit your salt intake and in all likelihood don't have to worry about consuming too little either. Use Himalayan or Halite (rock) salt to avoid possible contaminates.

What Is Salt?

Salt is usually referred to as common salt, mineral salt or table salt to distinguish it from the many other kinds of chemical compounds called salt(s). It is used as an ingredient in cooking and added to food when eaten, to improve flavour. It is also used as a food preservative and has many other uses in the chemical and other industries. Salt is a mineral compound of two chemical elements: Sodium (aka Natrium (Na)) and Chloride (Cl). Thus salt has a chemical formula of NaCl, typically made up of 40% sodium and 60% chloride.

The sodium and chloride in salt are both essential minerals required to sustain life. In the nutrition and medical fields, these essential minerals are referred to as electrolytes; you can find out more in the electrolytes article. Sodium also plays a role in maintaining your body's fluid balance.

Your kidneys help regulate your body’s sodium levels by adjusting the amount that is excreted in your urine and/or by retaining water within the body. These processes are used to maintain the specific sodium to water ratio your body requires. You can also excrete or 'lose' sodium through sweating, vomiting and diarrhoea - processes which occur independently of the kidneys, which may interfere with the regulatory function of the kidney's.

Typically, most of our intake comes from the processed, packaged and prepared foods we buy and consume, rather than what we add when cooking or eating food.

Health Concerns

These all relate to the sodium in salt rather than the chloride. Chloride does not appear to present any health concerns (although as with almost everything, a significant excess or insufficiency, if sustained or extreme enough will be harmful.)

Chronic Overconsumption

The health impacts of chronic (1) sodium overconsumption are apparently significant - but not everyone is equally susceptible.

frequent, ongoing, long term, extended (osteoporosis, cancer)

Eating too much salt can lead to all the health problems high blood pressure causes, including heart disease, stroke, kidney disease and some types of dementia. ¹

The recommended daily maximum salt intake (actually sodium intake) from various sources is;

World Health Organisation: 5g per day (2g sodium) ²
Blood Pressure UK: 6g per day (2.4g sodium) ¹
NHS UK: 6g per day (2.4g sodium) ³
American Heart Association: maximum of 5.75g (2.3g sodium) and an ideal of 3.75g (1.5g sodium) ⁴

I would typically complain these population-level averages are just that and along with all averages, are a convenient oversimplification which in no way applies to significant parts of the population (no-one actually has 2.4 children). However, in this case, the minimum amount of sodium the human body requires on a daily basis seems to be around 0.5g or less, so this recommendation seems likely to cover a larger majority of the population than most. This is supported by the fact the recommendation is a maximum (rather than an amount or minimum as most are) which also would appear to demonstrated the seriousness with which the risks of overconsumption are treated within the medical field.

The maximum is so high because a large part of the worlds population already significantly exceeds the recommendation and presumably this higher than desired level is considered achievable. Regardless, even this level of consumption is controversial; assuming you are not part of a high-risk population, there are a number of recent studies that suggest reducing intake to the recommended levels has no benefit in healthy individuals ⁵ ⁶ and may even be harmful ⁵ ⁷.

Particular salt-sensitive populations are more likely to experience the negative impact of over-consumption, these include;

those of African decent
those with high blood pressure (hypertension)
those with metabolic syndrome (diabetic and/or obese)
those of older age (60+ we imagine)
those with kidney disease

On the flip side, some factors that may increase your intake requirements of salt and other electrolytes include;

activity that causes you to sweat for a prolonged period (e.g. working in the sun/a hot environment all day or continuous exercise of 2hrs or more)
drinking large qualities of water or alcohol or taking diuretic medication (which increases the production of urine)
recent sustained episodes of vomiting or diarrhoea
starvation
bulimia or anorexia nervosa

In summary: if you are healthy and have normal blood pressure - regardless of your diet - you probably have no need to limit your salt intake and in all likelihood don't have to worry about consuming too little either.

Acute Overconsumption

Consuming a significant amount of sodium in a single meal or over a short period of time can lead to the following, temporarily;

Water retention - your kidneys attempt to maintain a very specific sodium to water ratio in your blood and will retain water in your body (rather than excreting it in urine) in order to do so
Rise in blood pressure - this is related to the water retention described above
Thirst - this is your body calling for more water so it can maintain the very specific sodium to water ratio required in your blood

Should your body's blood sodium levels rise above a safe level you will likely suffer hypernatremia. This condition can lead to;

thirst
decreased urination
weakness
nausea & loss of appetite
muscle twitching
confusion
bleeding in and/or around the brain & seizures
coma
death

The amount of salt a healthy person would need to consume to risk death is around 0.5 to 1 grams per kilo of bodyweight, in a single day.

Blood Pressure

If you do have high blood pressure (are hypertensive) or are a member of an at risk group then it does make sense to adhere to the recommended maximum intake (or less). Salt consumption causes high blood pressure as your kidneys attempt to maintain a very specific sodium to water ratio in your blood and will retain water in your body (rather than excreting it in urine) in order to do so. It's this water that increases your blood pressure (you quite simply have more more water in your blood).

In addition to that, maintaining a healthy lifestyle can also help;

exercise - ideally a combination of;
- dynamic (resistance lifting, push ups)
- static resistance training (isometrics (e.g. yoga, pilates, planks etc.))
- cardio
a (mostly) healthy, wholefood and ideally homemade diet - specifically consuming fruit and vegetables (which contain potassium and magnesium (electrolytes), as well as other essential micronutrients such as vitamins) - milk and yoghurts also contain potassium
adequate sleep and rest
meaningful and fulfilling social, familial and romantic relationships
avoiding or minimising alcohol, nicotine and recreational drug use, as well as your exposure to contaminates & toxins

As you may have figured out, potassium may help to reduce the effects of sodium for those that are salt-sensitive. The more potassium you consume, the more sodium your kidneys will remove through your urine. Potassium also helps to ease tension in your blood vessel walls, which helps lower blood pressure further.

Osteoporosis

A number of different studies have come to opposing conclusions concerning;

high sodium intake increasing calcium excretion which may lead to conditions such as osteoporosis, particularly in women⁸
low sodium intake leading to conditions such as osteoporosis, particularly in women⁷

Contamination

Sea salt is commonly (and increasingly) contaminated with:

microplastics
lead chromate

The best and likely cheapest and most easily available option to avoid this is Himalayan rock salt which is slightly pink in colour (due to it's iron content) and mined in Pakistan. As that suggests, there's little chance of microplastic contamination as the salt has been in the ground for a very long time and has not been exposed to used and degrading plastics dumped in the sea. Rock salt is still originally from the sea of course, but was deposited where it now lies long before plastics were invented.

The mineral rich nature of Himalayan salt also apparently makes it very good. Refined sea salts (of the kind you'd typically find in a supermarket or grocery store) are generally processed to remove these minerals.

You can also likely find Halite (rock salt) which is often grey in colour but will also be devoid of these contaminates and will also likely be unrefined.

I've seen mention of French salt (such as Fleur de sel de Guérande) as an alternative but this is still sea salt.

Fortification

Salt, due to it's widespread consumption, is often fortified with miniscule (measured in parts per million (ppm)) amounts of iodine (in the form of potassium iodide, sodium iodide or sodium iodate) in countries with populations that are usually deficient. An iodine deficiency will likely lead to goitre, which is a lump or swelling at the front of the neck caused by a swollen thyroid. Dextrose may also be added to stabilise the iodine. Salt is not commonly fortified with iodine in the UK or the US.

Other possible fortifications include iron, folic acid and fluoride (France).

Additives

Most supermarket or grocery store bought salt that isn't sold in a grinder or mill will contain a tiny amount of one or more of the following in order to avoid water retention and/or allow the salt to flow freely - these are usually referred to as anticaking agents;

magnesium stearate (E470b)
sodium ferrocyanide (E535–538)

Further Information

Obligatory Wikipedia links for: (salt), sodium chloride and chloride).

Random Facts

Salt is;

alkaline
a metal

Sodium has positively charged ions, chloride has negatively charged ions.