Dear Doctor: Can patients with chronic kidney stones reduce their likelihood of problems by adding daily magnesium to their diet?

Dear Reader: There are many hypothetical reasons why supplemental magnesium could decrease the chance of kidney stones.

Kidney stones are quite common, with 10 percent of people in the United States developing them over their lifetime. And the rates are increasing. In fact, the incidence of kidney stones has nearly doubled over the last 30 years. The majority of stones (65 percent) are calcium oxalate; 15 percent are calcium phosphate; and the rest are uric acid or struvite. Thus, the medical community has looked for ways to decrease the amount of calcium in the urine as well as its ability to form crystals there.

Theoretically, magnesium could decrease the possibility of stone formation by binding to oxalate in the intestine, leading to less oxalate in the urine and possibly fewer calcium oxalate stones. It also could bind to oxalate once it's in the urine, enabling the oxalate to be excreted before it binds with calcium. Magnesium preparations could increase urine levels of citric acid, which could bind the calcium and lower the amount of free calcium in the urine. And magnesium could decrease the ability of calcium oxide to form crystals in the urine.

I say "theoretically" for a reason, however. Magnesium also inhibits the reabsorption of calcium by the kidneys, leading to more calcium in the urine and thus a greater chance of kidney stones. (This risk is greater when the urine is overly acidic and less so when the urine is more alkaline.) And while magnesium may increase the amount of calcium in the urine, animal studies have shown that a lower level of magnesium in the urine is actually associated with a greater risk for kidney stones.

In a 2017 study at the University of Texas, researchers analyzed the impact on women of various amounts of dietary magnesium lactate, potassium citrate (which alkalinizes the urine) and ammonium chloride. The goal was to assess how magnesium intake and the pH of urine could affect kidney stone risk. As expected, making the urine more alkaline decreased the calcium excreted in the urine, but did not decrease oxalate in the urine. The magnesium lactate actually increased urine calcium -- even with the addition of potassium citrate -- as well as the risk of calcium oxalate stone formation.

I'm not sure what supplement you've used, but not all supplements would have the same effect as magnesium lactate. Magnesium oxide, for example, provides less magnesium than magnesium lactate, which alkalinizes the urine.

One interesting note from the 2017 study is that magnesium lactate decreased the amount of phosphorus in the urine and thus may decrease the formation of calcium phosphate stones. I'm not sure if your stone was identified as containing calcium phosphate, but that may be interesting to know.

Ultimately, however, there are no good controlled trials assessing whether magnesium has any effect on people with kidney stones, so I can't make a general recommendation. Clearly, more study is needed.

(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. Owing to the volume of mail, personal replies cannot be provided.)

Dear Doctor: I retired from a demanding desk job last year and, at age 65, have had to face the facts -- I have become sedentary and need to lose at least 20 pounds. My wife is helping me out with a more healthful diet. But my son says that in addition to the swimming and cycling program I'm on, I need to start lifting weights. Why aren't the pool and the bike enough?

Dear Reader: We'd like to congratulate you on your retirement and on your commitment to improving your health. It's all too easy to let the demands of work take precedence over self-care, and getting fit again can be a challenge. You're fortunate to have a supportive wife -- and a savvy son. Recent research shows that he's on the right track with his advice about adding weight training to your exercise regimen.

When it comes to body weight, it's not just what the scale says that matters. The percentage of lean muscle mass to body fat is an equally important metric. But as we age, the metabolic changes that take place mean we also lose muscle mass. So even if someone weighs the same at age 65 as they did at age 35, the composition of their body is not the same. Muscle mass has decreased and body fat has increased, a change that leads to a net drop in metabolic rate.

The challenge for older adults who want to lose weight is that the body burns both fat and muscle when in a calorie-deficit situation. For every pound you lose, up to one-third of it may be muscle. And since muscle is metabolically more active than fat, each pound of weight loss actually makes it a tiny bit harder to lose the next pound. The challenge becomes how to lose fat while preserving muscle.

According to the results of a study published last year, one possible answer is to pair a weight loss program with weight training. Researchers from Wake Forest University in North Carolina studied 249 adults, all in their 60s, all of them either overweight or obese. The participants were divided into three groups that focused on different weight-loss regimens -- diet alone, diet and walking, and diet and weight training.

After 18 months, the group that walked and the group that lifted weights lost 16 and 17 pounds, respectively. The diet-alone group lost 10 pounds. But when it came to loss of muscle mass, the walking group had the highest numbers. The diet-and-walk group lost 4 pounds of muscle mass. The diet-only and the weight training group each lost about 2 pounds of muscle mass.

Preserving muscle mass, which helps with balance and agility, becomes particularly important as we age. And weight lifting has other benefits as well: In addition to the metabolic boost, studies have shown that it can be as effective as yoga in conferring mental health benefits.

We think it's always a good idea to check in with your primary care physician before starting a new exercise program. And if you do take up weight lifting, please consider working with a trainer to be sure your workout is both effective and safe.

(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. Owing to the volume of mail, personal replies cannot be provided.)

Dear Doctor: I had several concussions when I was younger due to various sports activities, not to mention one singularly bad bike ride. Now I read that a single concussion can raise the risk of Parkinson's disease. Just how serious is this increase in risk, and should I be worried?

Dear Reader: Your concern is understandable. The association between severe and moderate traumatic brain injury and Parkinson's has been recognized for some time.

Severe traumatic brain injury is an injury that leads to a loss of consciousness or coma that lasts for more than 24 hours and is evident on a brain imaging test. Moderate traumatic brain injury leads to a loss of consciousness for one to 24 hours and is evident via imaging. What you're describing sounds more like mild traumatic brain injury, in which the loss of consciousness lasts from seconds to minutes and brain imaging studies don't reveal brain injury. The majority of people describe this as a concussion. The question posed by the study you reference is whether mild traumatic brain injury can lead to Parkinson's disease.

The study looked at data from the Veterans Health Administration database. Researchers first gathered data on 162,935 veterans with a history of TBI and 162,935 veterans with no such history; they then classified the injury as mild, moderate or severe. The average age of both groups was about 48, and the veterans were followed for 4.64 years on average.

Overall, veterans with traumatic brain injury had a 71 percent relative increase in the risk of Parkinson's disease compared to those without TBI. The veterans with moderate or severe TBI had an 83 percent greater risk of Parkinson's, while those with mild TBI had a 56 percent relative increase in risk. When the authors looked further at those with mild TBI who had no loss of consciousness, they still found a 33 percent risk of Parkinson's. However, this last data point wasn't considered significant due to the low number of people diagnosed with Parkinson's in this group. Of note is that people with TBI had greater rates of psychiatric disorders.

Now let's look at why traumatic brain injury would lead to Parkinson's disease -- and let's start with Lewy bodies. These abnormal accumulations of protein in the brain have been known to contribute to Parkinson's, and a component of these proteins, called alpha-synuclein, is seen in the cerebrospinal fluid of those who have had severe traumatic brain injury. In addition, autopsy studies have found an association between early-life traumatic brain injury and Lewy bodies in the brain.

This is an important study for veterans. Of the 20 million veterans alive today, an estimated 40 percent have some history of TBI and 82 percent of those are considered mild TBI.

That brings us back to you and the concussions you had in sports and the biking accident. Although the study showed a 56 percent relative increased risk of Parkinson's with mild TBI, let us think of this another way. After the age of 60, Parkinson's affects 1 in 100 people, so if we extrapolate the data for those with mild TBI, the rate of Parkinson's would go up only to 1.56 in 100 people.

Still, it's good to understand the association between TBI and Parkinson's because it may lead to earlier recognition and treatment of the disease. But no one should panic just yet over the risk of Parkinson's caused by prior traumatic brain injuries.

(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. Owing to the volume of mail, personal replies cannot be provided.)