As you age, your body's ability to absorb vitamin B12 from food slows—4 out of every 100 women ages 40 to 59 are B12 deficient, and many more are borderline. But celebrating another birthday isn't the only cause: Avoiding meat, taking certain drugs—like Metformin (commonly prescribed to people with type 2 diabetes or polycystic ovary syndrome) or some common heartburn medications—and even having weight loss surgery all up your odds. 

The result of coming up short on vitamin B12 can be anything from intense fatigue to wonky vision. If the symptoms below sound familiar, ask your doctor to run a blood test to check your levels. If they're low, a supplement or injections will have you back to your old self in a couple of weeks. 

© prevention.com