The little-known danger of this common diabetes medicine — and the simple way to protect yourself

Metformin is the one and only Type II diabetes drug I recommend. Derived from the ancient natural remedy, French lilac, metformin keeps blood sugar under control and helps ward off all the serious complications associated with Type II diabetes, such as eye, heart and kidney damage. Its major “side effect” is significantly reducing the risk of pancreatic cancer.

But it does have one drawback. As I always warn, it increases your risk of developing a vitamin B12 deficiency and possibly anemia. And according to a new study, the dangers are even greater if you’re over 65.

The study used data on more than 3,000 men and women with high blood sugar who took part in the Diabetes Prevention Program and the Diabetes Prevention Outcomes Study. The researchers measured vitamin B levels in all the participants at the study’s outset. Then, they measured them again at five years and at 12 years follow-up.

After five years, the patients taking metformin had lower vitamin B levels than patients who took the placebo. And there were twice as many actual B “deficiencies” in the metformin group. In fact, four percent of the patients on metformin had a B deficiency at five years follow-up, compared to just two percent of the patients on placebo.

Furthermore, vitamin B levels were “borderline low” in 20 percent of those taking metformin, compared to 10 percent of those taking placebo. And these percentages were low according to the current standards, which are designed to avoid outright vitamin B “deficiency” diseases. These guidelines aren’t geared to levels for optimal health.

Prolonged vitamin B deficiency is serious business. It can lead to nerve damage, impaired cognition, dementia, and anemia. But it’s relatively common in the U.S., with an estimated three million new cases each year.

Here’s why I think many people get into trouble with the B vitamins: They’re water-soluble, so you can’t store them. B12 is especially important as it’s the “energy” vitamin. In Europe the Bs are called “neuro-vitamins.”

You can get some vitamin B from the diet. Eggs, dairy and meat are all good sources. But vegetarians have a high rate of deficiency. And most natural sources contain much lower levels of B vitamins today than they did 30 years ago. So supplementing daily with a high quality B complex is a good option for most people.

If your urine turns yellow, try this…

Some of my readers observe they have yellow color in their urine sometimes when taking a daily B complex. Indeed, the yellow color occurs because your body excretes excess vitamin B (since again, it can’t be stored).

If you observe yellow color, try this at home…

After taking a B complex every day, if you observe a yellow color, just skip taking it for one day. The following day, start taking it again. Your urine will not be yellow on that second day. Your body will take up vitamin Bs that it missed the day before.

Most B vitamin dosages are formulated with optimal levels in mind for the “average” person. But people are different. This experiment shows that it’s better to get little more than you need every day (and excrete the extra harmlessly) than to never get quite enough any day.

Amazingly the FDA, the American Diabetes Association, and medical practice groups, do not have any formal recommendations in place for monitoring B levels in people who take metformin. But they should. Millions of people with Type II diabetes, gestational diabetes (during pregnancy), polycystic ovarian syndrome, and other conditions take it every day. So that means many millions of people run the risk of developing a B vitamin deficiency.

And it’s really very easy to measure B vitamin levels. Just ask your doctor to add it to the list when you get your annual blood work.

It’s also very easy to make sure you’re getting enough of these essential nutrients. Simply take a high-quality B complex supplement daily. I find most people need it. Research shows it does a world of good for your body and mind too, especially if you take metformin for blood sugar control.


  1. “Long-term Metformin Use and Vitamin B12 Deficiency in the Diabetes Prevention Program Outcomes Study,” J. Clin. Endocrinol. Metab. ( 4/22/2016