Some studies generally indicate a link between higher salt intake and blood pressure, and other studies show a link between higher blood pressure and higher likelihood of cardiovascular disease.
The most persuasive type of study to answer the question of the link between salt and CVD and other ailments would probably be a long term (decades long) randomised controlled trial (RCT).
Randomised controlled trials are considered the gold standard of clinical trials, because they involve a strict methodology to avoid selection biases.
In an RCT, the sample (ie a subset of a population) is selected randomly into a control group (no intervention, or a placebo intervention), and a treatment group (receives intervention).
The two groups are followed up and then the results are analysed. The RCT allows us to investigate the contribution of the intervention to the outcome, while isolating the influence of any other variables.
An RCT (randomised controlled trial) for salt intake might involve two groups – one on a low salt diet and another on a high salt diet, and followed for twenty years.
An RCT on salt intake of that length and rigour does not exist – and similarly, there are no RCTs on smoking. The outcome is we have to make our judgments from less-than-gold-standard evidence.
But the consensus view in literature is uncontroversial: an increase in risk of cardiovascular disease for every extra gram of sodium eaten per day.
Source: Nutritionfacts website