Dear Doctor: I am an 88-year-old man who, until recently, played a decent game of golf twice a week. Then, about 18 months ago, I began to experience weakness throughout my body, especially in my legs. Casual research indicated that Crestor, a statin I have taken for several years, was likely to blame. My doctor took me off Crestor two months ago in hopes that the condition would reverse, but any improvement is insignificant. Why do doctors prescribe debilitating drugs with no regard to side effect warnings?

Dear Reader: Pharmaceuticals are a large part of a doctor's armamentarium in treating and preventing disease. The medication you mentioned, Crestor (rosuvastatin), is one of many statins used to lower cholesterol. These medications are beneficial in decreasing the possibility of heart attacks and strokes in people who are at risk, as data have repeatedly born out.

But statins also can lead to mild or debilitating muscle aches in 1.5 to 5 percent of people taking them. In rare cases, they can cause a severe breakdown of muscle, a condition known as rhabdomyolysis. Theoretically, water-soluble statins such as rosuvastatin, pravastatin and fluvastatin are less likely to cause muscle aches; in fact, I've seen rhabdomyolysis twice with Crestor.

As your doctor knows, when a patient experiences muscle aches while taking a statin, the best course of action is to stop taking the drug. Sometimes the reduction in muscle aches is immediate, sometimes not. The average time that it takes for people to develop muscle aches with a statin is 6.3 months; the average time it takes for the muscle aches to improve after stopping a statin is 2.3 months.

Patients should be warned about statins' potential side effects and be monitored for them. But to come back to your question concerning what a doctor should do about medications with both potential benefits and potential side effects, my answer is don't overprescribe them.

As for statins, many in the medical community advocate their use for a large swath of the general population, often using cardiovascular risk calculators to estimate a person's chances of a heart attack and thus their need for a cholesterol-lowering medication. However, preliminary findings from a 2016 Kaiser study question the efficacy of the calculator, which means many doctors who make statin recommendations may be overestimating the risk of a cardiovascular event.

That said, statins are far from the only commonly prescribed drugs with a substantial risk of side effects.

Anti-hypertensive medications, which effectively lower the risk of heart attacks and strokes, can pose additional problems. Thiazide diuretics can lower sodium levels, sometimes to dangerous levels, leading to hospitalization and even death, while ACE inhibitors and angiotensin-receptor blockers can elevate potassium levels and cause abnormal heart rhythms.

Opiates control pain in the short term but can be abused in the long term. And, of course, chemotherapy, while curative for many cancers, often has severe side effects.

While doctors can't go through every potential side effect of a medication, they do need to take the time to describe the most common risks. And they need to be careful in not overprescribing medication.

(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 know that all sorts of studies show that fiber is good for you, but has anyone figured out the reason why?

Dear Reader: You're right -- the upside of fiber has been with us for quite a while now. Not only has the list of proven health benefits continued to grow, but also the language itself has changed: It used to be referred to as "roughage." But whatever it's being called, fiber is basically the carbohydrates in our food that resist digestion. And though there has been plenty of educated guessing about why we do measurably better over the short and long haul with a regular supply of fiber in our diets, a definitive answer has proven elusive. Now, however, ongoing research into the gut microbiome is offering up some intriguing answers.

First, some of what researchers had already believed about fiber's benefits continue to hold true. Foods that are high in fiber help to slow the absorption of sugars during digestion, which is a boon in regulating blood sugar levels. As a result, fiber in the diet can be a hedge against developing diabetes. Fiber makes you feel full after a meal, helps lower inflammation, and its presence in the intestines aids in elimination. Research shows that a diet high in fiber results in lower rates of heart disease and certain cancers, which may be why eating lots of fiber has been linked to a longer life span in general.

What's really interesting is scientists are now discovering that the fiber we consume feeds the billions of microorganisms each of us hosts in our bodies. Better known as the gut microbiome, it's becoming clear that they play an important role in keeping us healthy. If that number sounds like a lot, you're right. It's now estimated that these tiny hitchhikers make up between 1 and 3 percent of a person's total body weight. That means if your scale says 135 pounds, up to 4 pounds of that weight is beneficial bacteria. And since both quantity and diversity of beneficial bacteria are equally important, making sure they stay fed and happy is key.

Recent studies suggest that the way to cultivate a strong gut microbiome is keeping it supplied with plenty of fiber. When mice were put on a diet loaded with fat and low on fiber, the number and diversity of bacteria in their guts plummeted. At the same time, the mice themselves underwent changes that adversely affected their health. Not only did their intestines shrink, the protective coating of mucus along the intestinal walls became dangerously thin. This woke up the immune system and triggered an inflammation reaction. In time, this chronic inflammation was associated with weight gain and unhealthy blood sugar levels.

Bottom line -- the fiber you consume feeds the beneficial gut bacteria that help to keep us healthy in ways we don't yet fully understand and have yet to discover. So, when you're having that salad of leafy greens, a handful of walnuts, an apple or banana, or a serving of beans, you're not just eating for one -- you're eating for a few billion.

(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: 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.)