Dear Doctor: Everyone in my partner's family loves coffee, but I'm like the rest of my family -- we can take it or leave it. Is it possible that a love of caffeine is in their genes?

Dear Reader: Surprising as it may seem, recent studies suggest that yes, for some people the craving for that first (and second and third) cup of daily coffee is actually built into their DNA. The bigger picture turns out to be even more interesting and a bit complex -- so first, a bit of background.

According to the National Institutes of Health, caffeine is the most widely used stimulant in the world. Found in coffee, tea, chocolate, colas, energy drinks and some medications, caffeine gives you a lift because it blocks a brain chemical called adenosine, which causes sleepiness.

Whether coffee is good or bad for you has been a source of conflicting medical opinion for quite a while. For every new study that finds the good -- increased concentration, elevated mood, decreased risk of some cancers and chronic diseases -- there's another study to highlight the bad. Coffee consumption has been linked to anxiety, insomnia, high blood pressure and an increased risk of heart attack.

Is the science on both sides of the caffeine debate wrong, or is it possible that something else is going on? In fact, scientists now believe your question hints at the answer. Not only does your DNA decide whether or not you will love coffee, the genes you carry determine how coffee will affect your body and your health.

In a study published in 2014, researchers compared coffee drinking habits among large groups of people of European and African-American descent. They also did genetic studies on each group. What they learned is that the ways in which you respond to coffee -- whether it wakes you up, makes you jittery, gets you inspired or gives you the shakes -- is coded into your genes. Depending on your specific genetic makeup, your body is either good at processing caffeine, or isn't efficient at all.

People in the study with the "fast" gene, which helps the liver to break down caffeine quickly, drank far more coffee than those with the "slow" gene. Researchers think that's because caffeine leaves their bodies so quickly, it takes a lot more coffee to keep the buzz going.

When scientists separated coffee drinkers into two groups, one with the fast gene and one with the slow gene, they had an aha! moment. The fast gene group of coffee drinkers actually showed a decreased risk of heart attack and hypertension. But people with the slow gene, which lets caffeine linger in the body and create more chemical interactions, had a greater risk of heart attacks and high blood pressure.

So barring a DNA test, how do you know how much coffee per day is safe to drink? Considering the many types of coffee-based drinks on the market right now, each with a different potency, it's best to think in milligrams.

Total caffeine in a cup of coffee, for example, can range anywhere from 50 to over 400 mg. Current wisdom is up to 400 mg of caffeine per day is a safe upper limit for healthy adults. But if even a cup of weak diner coffee gets your heart racing, then decaf -- or a glass of water -- is the safer bet.

(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: 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.)