Dear Doctor: One of my resolutions for the new year was to become a vegan, and now my girlfriend is saying I'll have to take supplements to get enough vitamin B12. Why can't I get B12 in my diet, and what will happen if I fall short?

Dear Reader: Your girlfriend has done her homework -- vitamin B12 is a nutrient that is essential to human health. And while it occurs naturally in a wide range of animal foods, B12 is not found in any plant foods. As a vegan, you're now going to have to rely on supplements to be sure you get enough B12.

Why is it so important?

Vitamin B12 is a bit of a workhorse. Not only does it play a key role in the proper functioning of the brain and the nervous system, it's crucial to the production of red blood cells in the bone marrow. As though that wasn't enough, B12 also aids in DNA and RNA synthesis, and is involved in the metabolism of carbohydrates, fats and proteins. Research shows that B12 also has a hand in maintaining mood and memory.

The body does not store B12, so you need to ingest it every day. Beef liver and clams have the highest concentrations of the nutrient. It is also present in varying quantities in red meat, eggs, poultry, shellfish, milk and milk products. Many breakfast cereals and some dairy products are fortified with B12. For vegans, there are non-dairy milks, meat substitutes and nutritional yeast products to which B12 has been added. Dietary supplements are widely available.

What happens when B12 is in short supply?

Considering all the roles the nutrient plays in health and well-being, the list of symptoms is long and sometimes quite serious. People with a B12 deficiency may feel weak and tired, the result of the vitamin's role in producing the red blood cells that carry oxygen throughout the body. Since B12 helps maintain the protective sheath around your nerves, a lack of the vitamin can lead to strange sensations like numbness or tingling, as well as problems with balance or walking. Mood and memory may also suffer.

In extreme cases, B12 deficiency can lead to megaloblastic anemia, a blood disorder in which the red blood cells produced in the bone marrow are unusually large, malformed and immature.

And while your girlfriend is right about your need for vigilance in getting enough B12, she may do well to examine her own B12 status. Recent studies suggest that up to 40 percent of the population, vegan or not, may be flirting with B12 insufficiency. Due to physiological changes associated with aging, the elderly are at increased risk of vitamin B12 deficiency. Individuals who have undergone weight-loss surgery must also make a special effort to get enough of the nutrient.

As for you, a newly minted vegan, we recommend that you seek professional advice, preferably from your family doctor, to be certain that you forge a wise nutritional course.

(Send your questions to askthedoctors@mednet.ucla.edu, or write: Ask the Doctors, c/o Media Relations, UCLA Health, 924 Westwood Blvd., Suite 350, Los Angeles, CA, 90095.)

Dear Doctor: Many doctors in my area recommend CoQ10 in conjunction with statin drugs to reduce or eliminate muscle pain. It has worked for my wife, and we have heard lots of anecdotal evidence from friends who use it. What's the evidence behind the use of CoQ10 with statins?

Dear Reader: First, let's take a look at statins. These drugs have been repeatedly shown to lower cholesterol levels -- leading to decreased rates of atherosclerosis, heart attacks and strokes -- but they can have side effects. The most common side effect I've seen among my patients is muscle pain, which is the reason that most people stop these very beneficial drugs.

Now let's look at CoQ10. This coenzyme is needed for energy production within muscle cells. Some studies have shown that statins decrease the concentration of CoQ10 in both muscle tissue and in the bloodstream. The hypothesis is that, if you decrease the CoQ10 levels, you reduce the production of energy in muscle cells and they won't function as well, leading to muscle aches, weakness or inflammation.

In extremely severe cases -- I've seen this in very few of my patients -- statins can lead to the death of muscle cells, and a decrease in muscular CoQ10 may be one of the reasons. Massive cell death can also lead to acute kidney failure, but fortunately, in most cases, after stopping the statin and getting intravenous fluids, the patient's symptoms will quickly improve.

As for whether taking CoQ10 can prevent the side effects of statins, the studies of CoQ10 supplementation with statins are small and not conclusive. A 2007 study in the American Journal of Cardiology showed a 40 percent decrease in pain among statin users who took 100 milligrams of CoQ10 daily versus those who took 400 international units (IU) of vitamin E daily. However, there were only 18 people in the group that took CoQ10, so it's difficult to make an overarching conclusion about CoQ10's benefits. Other small studies have not shown any benefit from supplementation.

A combined analysis of six studies published in 2015 in Mayo Clinical Proceedings found a slight decrease in pain among statin users who took CoQ10, but the decrease was not clinically significant. The authors concluded that a larger study was needed.

Based on these studies, and the lack of a large study to evaluate CoQ10, it would be difficult to recommend CoQ10 to prevent muscle pain. However, judging by some of my patients' experiences and by your wife, some statin users have found significant pain relief with CoQ10.

My general thought on the matter is, if you have muscle symptoms with a statin, you should probably change the type of statin you're getting. Some types, such as rosuvastatin and pravastatin, don't concentrate in the muscles as much as others, causing fewer muscle problems. Switching to them may have benefit. Taking 100 milligrams of CoQ10 may also have benefit, but again, a large trial will be necessary to further evaluate this.

(Send your questions to askthedoctors@mednet.ucla.edu, or write: Ask the Doctors, c/o Media Relations, UCLA Health, 924 Westwood Blvd., Suite 350, Los Angeles, CA, 90095.)

Dear Doctor: I'm just about to turn 60, which -- from what I've read -- is when balance begins to become an issue. What can I do to stay steady on my feet?

Dear Reader: Although good balance is important to all of us who face the world on two legs, it's particularly vital to our well-being as we age. Unlike a child, who's likely to bounce right back up and laugh, or an adult, who comes away with a bump or a bruise, a fall for a senior citizen is a serious health risk.

According to the Centers for Disease Control and Prevention, one-fourth of people over 65 have a fall each year. In 20 percent of those falls, the outcome is a serious injury, including head trauma. At least 2 million elderly people per year visit the emergency room due to injuries from a fall. Close to 300,000 of them wind up in the hospital with a hip fracture.

At its most basic, balance is the ability to evenly distribute your weight and remain in control. We use our ability to balance when we stand, sit, walk, run and perform an infinite range of physical tasks. To achieve and maintain balance, our bodies use a complex set of systems that include muscle strength, sensory input like sight and touch, and a cluster of mechanisms in the inner ear that help with motion, equilibrium and spatial orientation.

To prevent a fall, start by reducing your risk. If you wear glasses, make sure your prescription is up-to-date. If you're on any medication, talk to your doctor about possible side effects that could affect balance.

At home, eliminate tripping hazards like uneven floors, loose rugs, stray power cords and clutter on floors. Be sure your home, both inside and out, is well lit. Install grab bars and non-skid mats in the bathroom. Keep a flashlight by your bed for nighttime emergencies.

Staying fit and flexible makes a big difference. When you get out of a chair, try rising without using your hands. Practice standing on one foot -- balance begets balance. Walking backward, which can be a surprising challenge, can help you become more spatially aware.

Yoga and tai chi have both been shown to help with balance. Slow and graceful, these exercises not only help to maintain balance, they can improve it. Weight-bearing exercises to strengthen the arms, back and legs are effective as well.

Many community centers offer a wide range of exercise classes specifically tailored to people who are older. It's a great way to get fit and meet people with whom you can exercise in the future.

And in case you have any doubt that now is a great time to start working on balance, an intriguing new study backs you up. When researchers analyzed 775 participants between the ages of 30 and 90 over the course of several years, they discovered that the decline in balance actually begins during your 50s.

(Send your questions to askthedoctors@mednet.ucla.edu, or write: Ask the Doctors, c/o Media Relations, UCLA Health, 924 Westwood Blvd., Suite 350, Los Angeles, CA, 90095.)