why does b12 have to be injected What You Need Know About Vitamin Sublingual B12 vs. B12 Injections:

When we don't get enough iron, we may experience: Reduced capacity to exercise and skeletal muscle atrophy, even before iron deficiency anemia (IDA) develops Over time, IDA, resulting in abnormal red blood cell formation and symptoms such as fatigue, weakness, difficulty concentrating, impaired cognitive and immune function, and poor body temperature regulation IDA has also been linked to impaired glucose metabolism---potentially due to poor conversion of proinsulin to active insulin in the body

However, many foods are fortified with vitamin B12, per Harvard T.H

Every released batch must have confirmed compound identity and raw material purity of 99% or higher

When Should You See a Doctor

Vernon Book Systems, 2016) ISBN 978-0-9818193-8-9 "What an Affliction": Mary Todd Lincoln's Fatal Pernicious Anemia"