It is a busy day at the retail pharmacy, where you work. You are at the cash register with a gentleman, CK, age 65 years, and he is picking up his prescription for metformin (Glucophage). You ask him if he has any questions about his medications.

He replies, “Yes, as a matter of fact, I do have a question that has been on my mind the last few months. My blood sugars have mysteriously been lower than normal, which I realize is a good thing. My doctor is very happy with my results, and apparently all my blood work has improved. I have no idea what is causing the improvements because I have not changed my diet or lifestyle at all. Up until this point, I have only been getting worsening news from my doctor. But mysteriously, things are turning around and improving.

CK continues, “My question for you is: are there any drug interactions that you can see on my profile list that are causing these good changes?”

You check the computer and see that he is on the following drugs:
  • Metformin 500mg BID
  • Linsinopril 5mg qd
  • Trazadone 50mg qhs prn sleep
  • Diclofenac 5omg qd bid-tid prn pain

You return to the counter and ask him about the over-the-counter products and the natural supplements that he takes at home. He says he just started taking vitamins in an attempt to strengthen his immune system due to the coronavirus disease 2019 (COVID-19) pandemic.

He reports the following products:
  • Multi-vitamin 1 qd
  • Vitamin D3 1,000 units qd
  • Vitamin C 1000mg qd
  • Polyethylene Glycol 3350 (Miralax), 1 capful qd to prevent constipation
  • Fluticasone (Flonase) nasal spray, 2 sprays in each nostril prn seasonal allergies.

Mystery: What is causing the good changes in this man’s blood work?


Solution: It is the new addition of vitamin C. The chemical structure of vitamin c and glucose are very similar and they compete for entry into the cell. Animals have the ability to convert glucose into vitamin c, but humans cannot do this.

The effect that vitamin C has on diabetes and insulin resistance is very complex, and investigators are still trying to understand the relationship. Taking 1000 mg/day or more vitamin C had a significant decrease in fasting blood sugar, triglycerides, low-density lipoprotein, glycated hemoglobin, and serum insulin. However, 500 mg vitamin C, did not produce any significant change in any of the parameters studied.


REFERENCE

Afkhami-Ardekani M, Shojaoddiny-Ardekani A. Effect of vitamin C on blood glucose, serum lipids & serum insulin in type 2 diabetes patients. Indian J Med Res. 2007;126(5):471-474.