Meat is a primary source of vitamin B12. However, a meat diet does not guarantee that a person is not B12 deficient. Elderly people, for example, can eat high quantities of meat and still have a deficiency of vitamin B12 because they do not have enough hydrochloric acid in their stomach to maintain the intrinsic factor. B12 deficiency is fairly common in elderly people who frequently have disrupted digestion. There appears to be something else causing B12 deficiency in older people which researchers have yet to explain.
Researchers do know that more people are deficient than currently appreciated.
When researchers at the Veterans Hospital in Oklahoma used modified criteria to test for B12 deficiency, they discovered B12 deficiency affected twice as many people as the previous testing. Those with sleep problems may need vitamin B12. Studies show that B12 causes an earlier release of melatonin at night, which resets the sleep-wake cycle. B12 acts directly on the pineal gland to provoke a faster release of melatonin. At the tail end of the cycle, B12 causes melatonin to drop-off faster.