Does he eat foods that are fortified with B12, on a regular basis? Many non dairy milks, processed meat substitutes, nutritional yeast....Or does he take any B12 supplements either by itself, or as a multi vitamin?
Tendonitis is more common with age, and usually a result of straining a joint--I'm now suffering from shoulder and bicep tendonitis myself, which started about 3 months ago. very painful, and my movement was very limited. I've gone to physical therapy, and continue to do specific exercises daily. It's gotten a lot better, but still a ways to go
Deficiency can manifest in many ways, usually neurological. The best test is testing MMA levels, which is rather new
Who should get tested for vitamin B12 (cobalamin) deficiency, and which is the best test to use: serum B12, methylmalonic acid (MMA), or holotranscobalamin levels?
nutritionfacts.org
Vitamin B12 deficiency is a lack of vitamin B12 in your blood. It happens if you aren't eating enough vitamin B12 or if you have trouble absorbing it.
my.clevelandclinic.org
Has he been vegan for health? I would think the doctor would have suggested B12 supplements. I will say, B12 is stored in fatty tissues and deficiency can take years to surface, if, one had good levels to begin with.
Either way, he really should be taking a B12 supplement. While there is debate on how much, taking 1000 mcg daily is optimal for those over 65, and excess is p'd out