Sodium carbonate is found in glass, paper products, soaps, cleaners and bubble bath solutions. I can't imagine why it would be in and products you would ingest.
Are you thinking of Sodium Bicarbonate which is baking soda? Lowers acid in stomach, blood, urine, etc. If you are on a sodium restricted diet you do NOT want to take sodium bicarb unless your doctor is aware.
Sodium carbonate is a food additive also (E500), anti-caking agent, raising agent and stabilizer.
don't use it if you have High blood pressure!
I think the food additive is sodium bicarbonate, as mentioned above. Sodium carbonate is toxic in large quantities. Also smells bad. I've never seen it in any food I've eaten, at least that I know of. But it is found in seaweed naturally, and seaweed products are in many foods, so sodium carbonate might show up in these foods. If not separated from seaweed by industrial processes, it shouldn't be harmful. While high levels of sodium are bad for people with high blood pressure, in the Orient they certainly don't include seaweed in that, but that's something we probably don't know about for certain, and it's possible the diet of people who eat seaweed regularly is so much better than the rest of us that it might be less problematic for them than for us. Diet is complicated, and full of unknowns.