Dear Doctor: If you don't have risk factors for having a heart attack, should you be taking aspirin every day?

Dear Reader: Let's consider the risk factors, how aspirin works and the numbers. The risk factors for having a heart attack include diabetes, high blood pressure, smoking, high LDL cholesterol (the so-called "bad" cholesterol) and age.

Aspirin decreases blood clotting within the vascular system by not allowing platelets to adhere to each other. This effect can be shown even with low-dose, or 81-milligram, aspirin, also known as baby aspirin. Daily use of standard aspirin has been shown to significantly benefit those who are having a heart attack and those who have had a heart attack in the past. For people who have a history of heart attacks, taking a low-dose aspirin will decrease the chance of having another heart attack by 20 percent.

However, if you're a 40-year-old who has never had a heart attack and has none of the above risk factors, your chance of having a heart attack is low. For you, aspirin will have little benefit, and may cause more harm due to increased chances of bleeding in the stomach and a small increased risk of bleeding in the brain.

If you're a 55-year-old who has good blood pressure, low cholesterol and does not have a significant smoking history, your risk is also low, so again there is little benefit to aspirin compared to its risk.

If you're 65 without risk factors, aspirin might reduce the risk of a heart attack, but that risk reduction is offset by the increased risk of bleeding in the stomach. The same is true for a 75-year-old. These gastric bleeds that happen with aspirin use can be severe and can lead to a need for blood transfusions. They can even cause death.

If further risk factors beside age are added, then the benefits of aspirin increase. So a 55-year-old with diabetes who smokes cigarettes would clearly benefit by taking a daily baby aspirin. This benefit outweighs the risk of a stomach bleed and the risk of bleeding in the brain.

More interesting -- for some people, anyway -- is that much of the mortality benefit seen with long-term aspirin use may be in decreasing colon cancer, not in its reduction of heart attack. People who take low-dose aspirin for more than 10 years can reduce the risk of colon cancer by 20 to 40 percent, studies have shown. In fact, the mortality benefits associated with aspirin -- in the general population -- may be more strongly linked to a decrease in colon cancer than to a decrease in heart attacks.

The bottom line: If you have low risk for a heart attack or have no family history of colon cancer, aspirin offers little benefit.

(Robert Ashley, M.D., is an internist and assistant professor of medicine at the University of California, Los Angeles.)

(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: If there's no proof that flossing is beneficial, do I really need to do it?

Dear Reader: You're referring to an article published by The Associated Press last summer, which revealed that the studies cited by the American Dental Association (ADA) and the American Academy of Periodontology to recommend daily flossing are scientifically inadequate. To say the story caused a ruckus is an understatement.

According to the AP investigation, the advice to floss daily is based on studies that are "very unreliable" and whose quality is "very low." Many of the studies were funded by dental floss companies, which opened up "a moderate to large potential for bias."

It's important to note, though, that while the AP story found fault with the research, it didn't offer evidence that flossing doesn't work. So while you could use the revelations as an excuse to ditch the dental floss, dentists and dental hygienists say that manually cleaning the space between your teeth is still a good idea.

Their reasoning? Each tooth has five surfaces. Three of these -- front, back and biting edge -- can be cleaned with a toothbrush. However, the sides of your teeth, which sit adjacent to other teeth and can capture food particles and bacteria, require a different tool for removing both plaque and debris.

Dental plaque, a clear film, is actually a mass of hundreds of different acid-producing bacteria that naturally form in the mouth throughout the day. When left undisturbed, plaque can give rise to cavities and gum disease. The only way to get rid of plaque is manually. That means brushing and, for the inner surfaces of your teeth, flossing.

Matthew Messina, DDS, a spokesman for the ADA, concedes that the existing research on the benefits of flossing is less than rigorous. When flossing is done properly, however, Messina says it remains the most effective way to remove damaging plaque from those hard-to-reach inner surfaces of your teeth.

If flossing is painful, then you're probably doing it wrong. Rather than a sawing motion at the gum line, proper flossing is a gentle, vertical sweep along the inner edge of each tooth. Messina recommends that you ask your dentist or dental hygienist to demonstrate proper flossing technique.

For optimal dental health, the ADA recommends brushing with a fluorinated toothpaste at least every morning and evening, and visiting a dentist for professional cleaning twice a year. Considering how little time it takes and what's at stake, dental professionals agree that flossing should continue to be part of your daily personal hygiene.

(Eve Glazier, M.D., MBA, is an internist and assistant professor of medicine at UCLA Health. Elizabeth Ko, M.D., is an internist and primary care physician at UCLA Health.)

(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: My daughter had the chickenpox vaccine as a child, so she never had chickenpox. She's now an adult. Should she get a booster?

Dear Reader: That's an excellent question. The chickenpox (Varicella) vaccination has been widely used in the United States since 1996. Given in a two-dose schedule at 12 to 15 months and at 4 to 6 years, the vaccine has significantly reduced the incidence of chickenpox among the population. If your child had the vaccine 20 years ago, she is indeed still protected from getting chickenpox.

But -- and this is concerning -- she's less protected than when she got the vaccination. That's especially important because contracting chickenpox as an adult can lead to an increased risk of pneumonia and even death.

Children in some pockets of the United States are less likely to have been vaccinated, and thus outbreaks of chickenpox occur. This is also true for other countries with more spotty vaccination rates than the U.S. A 21-year-old may be more susceptible to getting the virus if he or she visits those areas.

The good news is that, in most areas of this country and the developed world, the vaccine has significantly reduced the circulation of the chickenpox virus in the population, so your daughter will be less likely to be exposed to it. And you can take solace in the fact that, if your daughter does develop chickenpox, it probably won't be as severe as someone who was never vaccinated. That's because she does have some immunity from her previous vaccination, so she will be less likely to get the severe complications that can occur in adults.

That said, there are many unknowns regarding what will occur later in life when your daughter is in, say, her 50s and her immunity to the virus has waned further. Currently, neither the federal Centers for Disease Control and Prevention nor the American Academy of Pediatrics recommends a chickenpox booster. That could change over time -- especially for those people traveling to areas where chickenpox is prevalent.

We will understand more about the vaccine and its protective powers as this first generation of people who received the vaccine gets older -- and as doctors and patients ask these important questions.

(Robert Ashley, M.D., is an internist and assistant professor of medicine at the University of California, Los Angeles.)

(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.)