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Welcome to the Huel Forum!
About half of the calcium comes from the food ingredients and half from the micronutrient blend. We have a handy chart that breaks this down. The calcium that is added is in the form of calcium carbonate.
I think the relationship between calcium and cardiovascular risk is unclear. A 2023 meta-analysis found no correlation.
You can find a bunch of people talking about their experience running and using Huel on Reddit!