Dear Doctor: A recent study found that air pollution increases the risk of Type 2 diabetes. How can that be? Air pollution can't possibly raise blood sugar levels.

Dear Reader: I can understand your disbelief. My first thought when I saw this study was that it was correlative, not causative. In other words, air quality is simply worse in cities, which are more likely to have large numbers of people with lower socioeconomic status, who, in turn, tend to have greater rates of obesity and diabetes. Then I looked more closely.

Air pollutants assessed in the studies include nitrogen dioxide and particulate matter between 0.1 to 2.5 microns in size (PM 2.5). Early epidemiologic studies showed a correlation between areas of greater pollution and diabetes, but did not control for socioeconomic status. Then came a 2010 study that used census data from three counties in the United States, and assessed both rates of diabetes and Environmental Protection Agency data regarding PM 2.5 pollution.

The authors took into account such socioeconomic variables as median income, high school completion, male sex and ethnicity -- all markers for diabetes risk. The authors found a 16 to 20 percent increase in the prevalence of diabetes in the areas that had the highest amounts of PM 2.5 versus those areas with the lowest amounts, even with all other factors being equal.

Then came this year's study published in the journal Diabetes that included 314 obese Latino children in Los Angeles. The authors analyzed where the children lived; the amount of pollution to which they were exposed, measured by both nitrogen dioxide and PM 2.5; and their parents' socioeconomic data. The children were followed for 3.4 years, during which time they underwent tests of blood sugar, two-hour glucose tolerance, insulin and insulin response to glucose. The authors found that the markers for future diabetes were much greater in those exposed to greater amounts of pollutants. This was independent of socioeconomic status, and even independent of the level of obesity.

The cause isn't completely clear yet. Studies in rodents exposed to pollutants have shown increased inflammation within fat cells, accumulation of cholesterol in the liver and decreased ability of muscles to use sugar. This leads to both metabolic dysfunction and obesity. Further, pollutants can lead to systemic inflammation that in turn leads to insulin resistance, and thus the inability to bring sugar into the cells of the body, leaving it to sit in the bloodstream.

What is clear is that there does appear to be an association between pollution and diabetes, but more studies are needed to evaluate the degree of the association. Regardless, pollution is obviously unhealthy and needs to be controlled within society. The measurements of pollution provided in these studies come from the Environmental Protection Agency, whose existence is to safeguard the health of current and future societies.

(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 played a pretty rough game of tennis a few weeks ago and developed an ache in my right elbow that turned out to be bursitis. What can I do to ease the pain?

Dear Reader: Our skeletons are marvels of mechanical engineering. They create a scaffold for our muscles, skin and circulatory system, shelter our inner organs, and provide the leverage that makes it possible for us to move about. Wherever our bones meet, particularly in our joints, tiny fluid-filled sacs known as bursa act as cushions. They allow bones and connective tissue to glide easily over one another with minimal friction.

When injury, repetitive movement or sustained pressure causes one or more bursa to become inflamed, the resulting pain and tenderness are characteristic of a condition known as bursitis. Age can play a role in bursitis, as can rheumatoid arthritis. The pain arises when an injured bursa fills with excess fluid and then presses against surrounding tissues and nerves.

The most common locations for bursitis are the hip, knee, shoulder and, as you have discovered, the elbow. The condition is diagnosed via a physical examination of the area, and tests such as an X-ray or an MRI. When a physician suspects that infection may play a role in bursitis, she or he will take some fluid from the affected area for testing.

Since we're not sure what treatment you may have already received, we'll run down our approach with our patients. We begin by addressing the underlying cause, which is inflammation. Rest is important. Bursitis can be brought on by a specific activity, such as tennis for bursitis in the elbow, or throwing a ball or lifting a toddler for bursitis in the shoulder. We recommend that our patients refrain from the particular action until the condition has cleared up.

Anti-inflammatory medications such as aspirin and ibuprofen will help alleviate swelling and pain. If necessary, more powerful anti-inflammatories are available by prescription. Ice compresses applied for 15 to 20 minutes every four to six hours, for three to five days, can also be quite effective in managing the swelling and pain.

Less frequently, it becomes necessary to drain the excess fluid from the bursa with a needle and syringe, a procedure known as aspiration. If we suspect infection rather than injury plays a role, we will send the fluid out for analysis.

In many cases, bursitis will resolve itself over the course of a few weeks or, perhaps, months. In some instances, though, the pain may be persistent. When patients don't get relief from rest, icing and anti-inflammatories, the next step can be a cortisone injection into the site. Cortisone usually provides speedy relief from pain and can be targeted to a specific location.

We have found that gradually adding a gentle stretching program and some easy strengthening exercises can aid recovery. An elbow band, which reduces the pressure of the muscles in the forearm, can help with pain. Your family doctor will be able to help you with all of these.

(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: Some studies suggest that long-term calorie restriction can lengthen lifespan; others say it won't. Which should we believe?

Dear Reader: This is a perplexing question. We need energy to live, and the food we eat provides that energy. Obviously, gluttony can lead to dire health consequences, including Type 2 diabetes, obesity and high blood pressure, but less obvious is the case for decreasing caloric intake to below normal levels in order to improve health.

The benefit of calorie restriction was first seen in laboratory rats in the 1930s. Subsequent studies have shown that a 30 to 60 percent reduction in calories in mice and rats led to an increase in both the average and maximal lifespan of the rodents.

Of note, researchers found equal improvement in average lifespan among rodents that exercised to keep the weight down, but no improvement in maximal lifespan. In other words, if the maximal age of a rat is 2 1/2 years, the maximum age would increase to 3 years by calorie restriction, but would stay at 2 1/2 years by exercise.

Calorie restriction has shown benefits in chickens, spiders and even single-celled organisms.

The reason may lie in the reduction of the metabolic rate that occurs with calorie restriction. In reducing the metabolic rate, the body temperature decreases, as does the formation rate of damaging oxidative chemicals. These oxidative chemicals damage DNA, cell membranes and the protein within cells, and may be one of the reasons that bodies age. Also, calorie restriction leads to a decrease in blood sugar and body insulin levels.

As for whether the physical benefits of calorie restriction apply to humans, a 2016 study in non-obese males and females compared those who maintained their normal diets to those who had a 25 percent decrease in their caloric intake. The subjects were followed for 24 months. The calorie restriction group lost almost 16 pounds more than the control group. Further, people's moods improved significantly in the calorie restriction group, as did reported improvements in quality of life, sleep and sexual function.

When it comes to calorie restriction and longevity, note that in Okinawa, Japan, calorie intake is 17 percent less in adults and 36 percent less in children when compared to the rest of Japan. The rate of death from heart attacks, strokes and cancer is 31 to 41 percent less than the national average. This doesn't prove cause and effect, but it does suggest the need for additional research.

Clearly, calorie restriction seems to have benefits, but proving those benefits over the long term in our not-so-steady human lives? That's not easy. Certainly, however, in our world of plenty, we need to be mindful of the amounts that we eat.

(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.)