An interesting thing happended to me the first week of June: I found out I have a vitamin B12 deficiency. I'm not a vegetarian, I'm not a vegan -- I do eat meat products once a day and I eat red meat usually twice a week.
I found out because I signed up for a program here in Ontario to get complete physicals to those who do not have a family physician. So we signed up with a nurse practicioner about 30 km away. No more sitting in the emergency waiting room when wondering if the cold I have is maybe pneumonia or bronchitis. The first phase of the complete physical is a complete round of tests -- six vials of blood -- but my insulin level is okay, so is iron, my cholestral is a little high. I'll get more definitive information on the start of heart and circulatory system when the cardiologist comes back from summer vacation. But the NP called me in when she found I had the vitamin B12 deficiency.
So why is vitamin B12 important? It impacts red blood cell development, your metalobolism (and subsequently your energy level), and your circadian cycle (sleeping through the night!). It also affects your nervous system too.
On the NP's recommendation, I went to a health food store and got a substantial vitamin B12 supplement. Since taking it I've noticed a real increase in energy (I do stuff in the morning, afternoon, and evening), sleeping better (usually a solid four hours before stirring away for a needed run to the washroom), a change in appetite so that cravings for high-energy (and often high-calorie) foods have vastly decreased, more stamina when I'm out bicycling, and less tingling in my arms and hands.
I still have to find out why my body has gotten so bad at absorbing vitamin B12. The health food store owner said that as we age we produce less of the enzymes needed to absorb vitamin B12 from food. I don't know if there is any healthy way to reverse/ameliorate that.