Dear Doctor: My blood test results always include levels of HDL and LDL cholesterol, but what about lipoprotein(a)? Don't high levels triple the risk of a heart attack or stroke at an early age? If so, shouldn't doctors test for it?

Dear Reader: The short answer is: for some people, yes.

The longer answer starts with some background: Lipoprotein(a) is a type of blood protein similar to the low-density lipoprotein (LDL) commonly measured in a cholesterol test. Because its structure resembles that of the proteins plasminogen and tissue plasminogen activator (TPA), which are involved in the breakdown of blood clots, lipoprotein(a) competes with those proteins and decreases their ability to break down clots. In other words, lipoprotein(a) boosts the blood's clotting ability. This could potentially aid wound healing and repair of tissues, but no specific need for lipoprotein(a) has been found.

The big concern with lipoprotein(a) is its potential to encourage clot formation within the arteries, raising the risk of heart attacks and strokes. A 2009 study in the Journal of the American Medical Association reviewed the results of 36 studies assessing the role of lipoprotein(a) and vascular disease in a total of 126,634 people. The authors found that, with every 3.5-fold increase in the level of lipoprotein(a), there was a 13 percent relative increase in coronary heart events and a 10 percent increase in stroke rate. The authors concluded that the high lipoprotein(a) levels were an independent risk factor for heart attacks and strokes, but not as strong a risk factor as other cholesterol markers.

However, very high levels of lipoprotein(a) are a significant risk factor for coronary heart disease, as illustrated in an Italian population study. The 2014 study measured lipoprotein(a) in 826 people and then followed them for 15 years. Those with lipoprotein(a) levels greater than 45 mg/dl -- totaling 20 percent of the study group -- had 2.3 times greater odds of stroke or coronary heart disease compared to those with lower levels.

As for why some people have higher lipoprotein(a) levels than others, the answer is in our genes. Variations of lipoprotein(a) levels appear to be related to a part of a gene called apo(a). Two different variations in this gene can cause elevation of lipoprotein(a). A grouped analysis found that people with one of the variations had 50 percent greater odds of coronary heart disease, while those who had both variations had 2.5 times greater odds.

So, to answer your question: If you have a family history of early heart disease, your doctor should consider checking your lipoprotein(a) level, especially if you have no other risk factors. People who have had a heart attack without any other risk factors also should have their levels checked.

As for lowering the lipoprotein(a) level, niacin can do this at high doses (2 to 4 grams per day), as can cholesterol-lowering PCSK9 inhibitors. Note, however, that no studies thus far have assessed the benefits of doing so.

Instead, people with very high levels of lipoprotein(a) may find greater benefit in significantly lowering their overall cholesterol with statins. Statins won't lower the lipoprotein(a) level itself, but they provide greater health-related bang for the buck. Lastly, because elevated lipoprotein(a) levels increase the risk of clot formation in the arteries, people at high risk may also find it prudent to take aspirin as a blood thinner.

In summary, for most people, overall cardiovascular health should be the focus in reducing the risk of heart attack and stroke, not lipoprotein(a).

(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: My daughter has been talking about the merits of "raw water" -- and the perils of regular tap water. Could it be that people are really drinking non-sterilized or treated water? Isn't that dangerous?

Dear Reader: Thanks to a recent feature story in The New York Times about several companies in the United States that are selling so-called raw water, there's now a national conversation about this trend. The water referred to in the story is untreated, unfiltered and unsterilized. The purveyors claim it is bottled in the exact state that it emerges from certain springs, and attach all sorts of health claims to their products.

While these companies say that the water they sell is safe for consumption (it turns out that one of these vendors, who charges upward of $20 per gallon, is actually drawing from the very same aquifer that furnishes part of Oregon with tap water at a fraction of the cost), the idea that people would seek out so-called natural water is alarming.

The truth is that securing clean drinking water has been one of the great challenges throughout history. Untreated water can contain everything from parasites, viruses and bacteria to naturally occurring chemicals like arsenic. And while municipal drinking water certainly has its own share of black eyes, as the scandal in Flint, Michigan, has most recently illustrated, the idea that spring water is automatically safe to drink is naive and dangerous.

According to the Environmental Protection Agency and the Centers for Disease Control and Prevention, drinking untreated water puts you at risk for any number of pathogens such as E. coli, hepatitis A, Shigella, giardia and norovirus, to name just a few. Diarrhea, cholera, dysentery, typhoid and polio are all water-borne illnesses. Add in wild card pollutants like pesticides, farm waste runoff, carcinogenic compounds and leakage or even spillage from septic tanks -- all of which can leach into the ground miles upstream of a seemingly pristine spring -- and drinking "raw" water can become a genuine health risk.

Clean water is an international health issue. In developing nations, water contaminated with pathogens and pollutants accounts for 80 percent of all disease. According to the World Health Organization, more than 300,000 children under the age of 5 die each year from gastrointestinal illness associated with the lack of potable water. As any experienced backpacker will attest, drinking unfiltered, untreated or unsterilized water is a foolhardy gamble that can result in grave health consequences.

This isn't to say that public water supplies are perfect. According to a report issued by scientists with the National Resources Defense Council last year, the aging municipal infrastructure in the U.S. is taking a toll on water safety. Violations of the landmark Safe Drinking Water Act of 1974 range from inadequate testing and reporting to the presence of a host of contaminants in community water systems.

Still, in our opinion the so-called raw water movement is misguided. While some natural sources may indeed be perfectly safe, the health risks of drinking untested water from a spring or pond far outweigh the chances you take at your kitchen faucet.

(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: Would you kindly address the risks of e-cigarettes compared to regular cigarettes? I am opposed to both because of the potential for nicotine addiction and other health issues. Some of my adult relatives, however, are convinced e-cigs are not harmful, even though they clearly seem addicted.

Dear Reader: On the surface, e-cigarettes appear to be a good idea. After all, they contain no combustible substances to become residue and enter the lungs. Instead, the devices feature a cartridge filled with a nicotine liquid that is vaporized and inhaled. Nicotine concentrations vary in the cartridges from 6 to 24 milligrams per milliliter. E-cigarettes also contain propylene glycol, which is used to prevent the liquid from evaporating, and flavorings that make the vapor more palatable.

As for their safety, first, let's assess the risk from nicotine. It's true that nicotine raises the pulse rate and increases the workload of the heart, but while smoking cigarettes is a significant risk factor for coronary artery disease and heart attacks, nicotine does not appear to be the culprit. In fact, studies have shown that people who use nicotine replacements in the form of gum, lozenges or patches have no change in their risk of heart attacks. Note, however, that rates of nicotine toxicity have substantially increased since the introduction of e-cigarettes. This occurs when someone uses too much nicotine or when someone, such as a child, ingests the liquid in one of the vials.

Second, let's assess what we don't know: the long-term effects of inhaling e-cig vapor. Acute exposure to the vapor does lead to a small increase in lung flow resistance, and the vapor could lead to more inflammation of the airways. Surveys of students in Hong Kong and in the United States have shown an increased rate of chronic cough and bronchitis among those using e-cigarettes. The vapor itself does have trace amounts of carcinogenic compounds, but at much lower levels than in combustible cigarettes.

Because the risk for lung cancer would appear to be smaller for e-cigs than for traditional cigarettes, they definitely have the edge in that respect. Additionally, e-cigarettes, like nicotine gums and patches, can decrease the desire to smoke combustible cigarettes. Studies of people using e-cigarettes to stop smoking have found rates of smoking cessation of 7.3 to 12.5 percent. And even if e-cigarettes don't actually help people stop smoking, they could theoretically decrease the number of regular cigarettes consumed. So, for those who smoke cigarettes already, e-cigarettes could provide a health benefit.

The bigger problem lies in e-cigarettes' risk to young people. Studies have shown that adolescents and young adults who use e-cigs have three times the risk of initiating regular cigarette smoking than those who don't use e-cigs. This may be due to the nicotine, of course, but regardless, it points to the potential connection between e-cigs and a lifelong nicotine addiction, with e-cigs being a gateway. Because of this potential, many doctors and anti-smoking activists have advocated banning advertisements geared toward adolescents.

In summary, perhaps the harm to your adult relatives depends on their smoking status and age. In any case, allow me to reiterate: While e-cigs seem healthier than traditional cigarettes, the long-term health effects are not known.

(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.)