Dear Doctor: A new study said that prolonged antibiotic use is tied to colon polyps. But "prolonged" meant "two weeks or more." I had a couple of bacterial infections in a six-month timespan. How worried should I be?

Dear Reader: Antibiotics have undoubtedly revolutionized medicine, saving countless lives against multiple types of bacterial infections. However, with antibiotics readily available and a society that craves a quick fix, antibiotics have been overused. For example, they are often prescribed needlessly for upper respiratory symptoms that are not due to bacterial causes. Such overuse has led to the formation of antibiotic resistance; alterations of normal bacterial populations in the intestinal, oral and nasal cavities; and unnecessary side effects from the antibiotics themselves.

As for whether antibiotics can increase the risk of precancerous polyps in the colon, let's look at the evidence.

The study to which you're referring, published this year in the journal Gut, reviewed the antibiotic usage of 16,642 female nurses age 60 or older. In 2004, the women filled out a questionnaire reporting the amount of antibiotics they used between the ages of 20 and 39 and between the ages of 40 and 59. In 2008, the women filled out another questionnaire reporting their antibiotic usage between 2004 and 2008. All the women had at least one colonoscopy between 2004 and 2010.

Researchers found that women who took antibiotics between the ages of 20 and 39 had an increased risk of colon polyps compared to women who hadn't taken antibiotics. The increased risk was relatively small for women who had taken antibiotics for only one to 14 days within that 20-year period, but the risk increased significantly -- by about 1.4 times -- among women who took antibiotics for 14 days to two months. That heightened risk didn't increase further among women who took antibiotics for greater than two months.

For women who took antibiotics between ages 40 and 59, the rate of colon polyps increased more dramatically and was more dependent upon the length of antibiotic use. Those who took antibiotics for more than two months had a 1.69 times greater risk of developing colon polyps compared to women who hadn't taken antibiotics. Because colon polyps can eventually lead to colon cancer, the findings are worrisome.

Additionally worrisome are the findings of a 2008 Finnish study of people ages 30 to 79 assessing their antibiotic use from 1995 through 1997. The researchers found that people who had six or more prescriptions of antibiotics in that two-year timeframe had a 15 percent increased risk of colon cancer.

A possible theory about why antibiotics may lead to the formation of colon polyps, and later cancer, could be because they indiscriminately kill healthy gut bacteria. As this occurs, other, more unhealthy bacteria predominate in the colon, which can affect its immune response, leading to disruptions in its lining and the formation of polyps.

So, yes, there does appear to be some increased risk of colon polyps with antibiotic use. I wouldn't be overly concerned about two courses of antibiotics, though I would be concerned for a multitude of reasons about a repetitive use of antibiotics. Such use raises the need to look for new ways to prevent, and treat, infections.

(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've always loved animals, and now I want to stop eating meat. But I'm 15 years old, and my parents think that's too young to make such a big decision. What can I tell them about being a vegetarian? I'm hoping I can persuade them.

Dear Reader: We think it's admirable that you want your lifestyle to reflect your beliefs. And we also understand how taking on a new diet might cause your parents to worry. As a teenager, you're in a period of growth spurts and hormonal shifts. Poor nutrition can affect your health, moods and learning ability. It may even play a role in susceptibility to disease in adulthood.

That said, the good news is that with proper planning, a vegetarian diet can be as nutritionally complete for people of all ages as one that includes meat. The vegetarian diet is often low in saturated fat and also high in dietary fiber. As a result, studies find that vegetarians often have a lower body mass index (BMI), lower blood pressure and more healthful cholesterol levels than people who eat meat. In addition, death from heart disease, stroke, Type 2 diabetes and certain cancers is lower among vegetarians than non-vegetarians.

You and your parents should start by deciding where on the meat-free scale of eating you wish to begin. Some vegetarians include milk and eggs in their diets. Vegans avoid all animal products, including honey and gelatin. And while it's not strictly vegetarian, some individuals skip red meat and poultry, but do eat fish and seafood.

When vegetarians decide to cut milk and eggs from their diets, alternative sources of protein, calcium and B12 become necessary. Protein can be found in soy products, beans, legumes and supplements. Small amounts of calcium are available in leafy greens and almonds. To get enough of the mineral, vegans often include calcium-fortified soymilk, juice and cereals, and calcium-set tofu in their diets.

Vitamin B12, found only in animal protein, is a vital nutrient. Your body needs it to make red blood cells, for proper neurological function, and to synthesize DNA. Vegetarians can get B12 in fortified products like cereals and soymilks, as well as in supplements.

Iron is a nutrient that vegetarians and meat eaters alike can fall short on. It helps your blood carry oxygen to muscles and organs, and is important for growth and normal cell function. Heme iron, which is most easily absorbed by the body, is found in lean meat and seafood. Nuts, beans, some leafy greens and fortified grain products are sources of non-heme iron, which the body doesn't use as efficiently. Vitamin and mineral supplements can help provide adequate iron, as well as other essential nutrients.

We've just hit the high points here. If and when your parents give you the OK to say goodbye to meat, we strongly recommend that you all become students of vegetarian nutrition. Your family doctor can help, and can also guide you to some excellent books and websites to help you plot your future journey.

(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'm 75 years old and have bruising on my hands, seemingly when anything touches them. I do not take blood thinners or aspirin. Occasionally I take an Aleve, which seems to make it worse.

Dear Reader: Such bruising is an annoying, yet common, problem as our bodies age. Many of my patients are flummoxed by the bruises on their skin, not even recalling any trauma that led to the purplish marks. Easy bruising as we age can be traced to several factors.

First, the distribution of fat changes. This is one of the crueler aspects of aging. Older bodies store more fat in the belly and lose the fat under the skin. This is most easily seen in the face, arms and in the back of the hands. Skin that has lost its subcutaneous fat has lost much of its cushion to absorb trauma. Without this cushion, the small blood vessels that course within and below the skin are more susceptible to direct trauma, leading to bleeding underneath the skin.

Second, the skin loses collagen, its most common protein. After the age of 20, a person produces 1 percent less collagen in the skin each year. So by the age of 75, the collagen loss is substantial. This causes the skin to become thinner and more fragile. Without this protection, the blood vessels underneath the skin are more prone to damage.

Third, the skin is less elastic. This means that the skin loses its ability to stretch and absorb external forces.

Finally, the small blood vessels within the layers of skin lose their elasticity as well. This increased fragility allows them to break with only minimal force.

To minimize the impact of these skin changes, you should be aware that the loss of elasticity and collagen are made worse by prolonged sun exposure. Using sunscreen on your arms and the backs of your hands will help to preserve the collagen and elastin within the skin. In addition, topical vitamins, such as vitamins A, E, C and B3 may also help to prevent sun damage. Lastly, smoking cigarettes also degrades collagen and elastin, so I would recommend not smoking.

You mentioned that you are not taking any blood thinners, but you are. Aleve (Naproxen) is a non-steroidal anti-inflammatory and, like all NSAIDS, thins the blood by reducing the ability of platelets to attach to one another. So that is why your symptoms are worse with Aleve. Supplements such as oral vitamin E or fish oil may also thin the blood, making you more susceptible to bruising.

If your bruising is accompanied by a reduced ability of your blood to clot -- which you would notice if you were to get a small cut -- you should consult a physician. This can occur because of blood thinners, but it can also be caused by a blood disorder.

In your case, I would recommend sun protection to the backs of your hands to decrease sun damage to the skin. Also, you should consider stopping Aleve and switching to Tylenol for pain relief; it doesn't have the same blood-thinning effect.

(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.)