Another big factor is stomach acid. As we age, our stomach acid gets exponentially weaker. This reduces absorption of nutrients and also minimizes the ability

Another big factor is stomach acid. As we age, our stomach acid gets exponentially weaker. This reduces absorption of nutrients and also minimizes the ability to destroy pathogens (not related to covid, just being complete). This becomes a circular problem, as the weaker stomach ph means less B1/zinc absorbed from all sources and less ability to produce stomach acid. This is why elderly often consume digestive enzymes or ACV to assist with digestion.