Is sea salt healthier than table salt?
No. Both are overwhelmingly sodium chloride, and the body cannot tell them apart. The differences are in texture, trace minerals and processing, none of which amounts to a health advantage.
Sea salt is produced by evaporating seawater. Table salt is generally mined from underground deposits — themselves ancient seabeds — then refined.
Sea salt retains small quantities of magnesium, calcium, potassium and other minerals, which is where the health claim originates. The amounts are nutritionally irrelevant. You would need to consume a quantity of salt far beyond any safe intake to get a meaningful contribution of any of them, and the sodium would do considerably more harm than the magnesium would do good.
By weight, the sodium content is essentially the same. By volume it is not, and this is the one practical difference. Coarse or flaky sea salt has larger, irregular crystals with air between them, so a teaspoon contains less salt than a teaspoon of fine table salt. Substituting one for the other by volume in a recipe changes the seasoning noticeably.
Table salt has one genuine advantage that is routinely overlooked: it is usually iodised. Iodine deficiency causes thyroid disorders and remains a real public health issue in many regions, and iodised salt is one of the most successful public health interventions of the twentieth century. Most sea salt is not iodised, and people who switch entirely can lose a significant dietary source.
Choose salt for its texture and how it behaves in cooking — flaky salt for finishing, fine salt for baking where it must dissolve evenly.
The amount of salt matters far more than the type; general guidance is to reduce total intake.