Dear Doctors: The whitening toothpaste I’ve been using for several years has a pleasant flavor and keeps coffee from staining my teeth. But I just realized it contains xylitol, which I’m hearing can cause heart problems. Do you know if this is true? Do I need to switch?

Dear Reader: Xylitol is an artificial sweetener that falls into a category known as sugar alcohols. Also known as polyols, these compounds contain neither ethanol -- that’s alcohol -- nor sugar. Rather, they are a form of carbohydrate with a chemical structure similar to sugar. In fact, their structure so closely resembles sugar, it triggers receptor proteins on the taste buds that are involved in identifying the flavor of sweetness.

Once activated, those proteins release molecules that stimulate nearby neurons. Signals travel to the region of the brain involved in taste, which interprets sweetness. In an interesting side note, cells from the sweet taste receptor system are scattered throughout the gut. They can detect nutrients and can tell the difference between natural and artificial sweeteners. Some researchers suspect that may play a role in why foods with artificial sweeteners can trigger rather than sate sugar cravings.

Sugar alcohols have from one-half to one-third the calories of natural sugars. Because they are metabolized slowly, they don’t take the same toll on the body’s insulin response as sugar. This has led to their widespread use in diet products, in foods suitable for people living with diabetes and for low-carb diets, such as keto. They are commonly used in diet sodas, sugar-free gum, baked goods and candy and even in some mainstream products.

From the moment these sugar substitutes reached the marketplace, they became a subject of study, debate and also controversy. Polyols occur naturally in small amounts in some fruits and vegetables. But for commercial use, they are lab-made. And as they find their way into a growing array of foods, the increasing intake per person is raising concerns. Investigations into various forms of sugar alcohols have found they can cause gastrointestinal problems such as pain, bloating, flatulence and diarrhea. Two years ago, an observational study linked them to an increased risk of heart attack and stroke.

And that brings us to a new study of xylitol, which pinged your radar. Published in the European Heart Journal, it analyzed blood samples from 3,300 participants who had completed an overnight fast. The researchers analyzed health data three years later, and they found that individuals with the highest blood levels of xylitol had twice the risk of having a heart attack or a stroke as participants with the lowest levels. The risk of death had also doubled.

As always, it is important to note that while an observational study can suggest a connection between certain factors, it can’t prove cause and effect.

In our own practices, we suggest artificial sugars should be used in moderation, and as a temporary aid. Toothpaste is not a significant source of xylitol and should not cause concern. However, if you are worried, you can switch to a natural toothpaste, some of which also have whitening varieties.

(Send your questions to askthedoctors@mednet.ucla.edu, or write: Ask the Doctors, c/o UCLA Health Sciences Media Relations, 10960 Wilshire Blvd., Suite 1955, Los Angeles, CA, 90024. Owing to the volume of mail, personal replies cannot be provided.)

Dear Doctors: We live in New Hampshire, and people are worried about Eastern equine encephalitis. There have been several cases, and someone has died. I’ve lived here all my life, and this disease is new to me. Can you please share what is known?

Dear Reader: Eastern equine encephalitis is a rare but potentially fatal mosquito-borne illness. Also known as EEE, it is one of four equine encephalitis viruses. The others are Western and Venezuelan equine encephalitis and West Nile virus. As with the other three, EEE originates in birds and rodents. It is spread to humans through the bite of an infected mosquito.

According to data shared by the Centers for Disease Control and Prevention, there are an average of 12 confirmed cases of EEE in humans in the United States each year. Occasional cases are reported in dogs, deer, horses and other farm animals. However, those animals, as well as humans, are what is known as a “dead-end host.” That means the concentration of EEE virus in the blood is too low to infect a mosquito, and thus cannot be passed on to another human. You also cannot become infected through contact with a sick person. Bottom line -- there is no human-to-human transmission.

As of this writing, there have been 13 confirmed cases of EEE in humans in the U.S. this year. They occurred in seven states, primarily in the Northeast. All 13 people developed severe disease, and two of them died.

Public health officials also track infected mosquitos, and that data has raised concerns. Spurred by a warming climate, the range of the mosquitos that carry the EEE virus is spreading. Infected mosquitos have been found in more than 20 states, primarily in the Northeast and Southeast. No infected mosquitos have been found farther west than Houston.

Not everyone infected with the virus becomes ill. When symptoms do occur, they typically begin four to 10 days after infection. The resulting illness can range from mild to severe. Initial symptoms include high fever, headache, muscle and body aches, joint pain, stiffness in the neck, fatigue and chills. EEE can escalate to cause neurologic disease, which affects the brain and spinal cord. This includes meningitis, which is inflammation of the membranes surrounding the spinal cord and brain, and encephalitis, which is inflammation of the brain Nearly one-third of these types of severe cases are fatal.

Diagnosis is based on the person’s symptoms and their potential recent exposure. When EEE is suspected, blood tests and analysis of spinal fluid will be done. There are no targeted medications for the disease, and treatment focuses on managing symptoms. This can include medications for fever, headache and pain, intravenous fluids and respiratory therapy. At this time, there is no EEE vaccine.

You can lessen the risk of any mosquito-borne illness by removing any sources of standing water around the home, which mosquitos need to lay eggs. Water trapped in a rain gutter or even an abandoned toy can become a breeding ground. And be sure to protect your body. Wear appropriate clothing and use an insect repellent when spending time outdoors.

(Send your questions to askthedoctors@mednet.ucla.edu, or write: Ask the Doctors, c/o UCLA Health Sciences Media Relations, 10960 Wilshire Blvd., Suite 1955, Los Angeles, CA, 90024. Owing to the volume of mail, personal replies cannot be provided.)

Dear Doctors: I would like to know why it is that so many medications have side effects. Is it the medications themselves, or is it the additives that are used in making them? Also, why do some people have severe side effects and others don’t have any at all?

Dear Reader: The answer to your question begins with a concept known as homeostasis. As with many medical terms, it has its roots in Greek: The prefix “homeo” means similar, and the suffix “stasis” means stable. The term was coined in 1926 to describe the dynamic feedback loops that allows the many -- and often competing -- physiological processes that contribute to health to remain in balance. Add in the fact they take place simultaneously, dictated by constant changes inside and outside of the body, and you get a sense of the complexity of it all.

Homeostasis starts at the cellular level. It includes functions such as the maintenance of pH levels and ion concentrations in the fluids inside and surrounding the cells; the manufacture of lipids, hormones and proteins; enzyme balance; the production and distribution of energy; and the safe transport and elimination of waste products. That is a pretty long list, and we’ve only scratched the surface.

If the body detects a potentially harmful imbalance, it sends out instructions with the corrections that are needed. The organs and tissues then respond, with the goal of maintaining homeostasis. These finely calibrated feedback loops oversee functions such as regulation of blood pressure, blood sugar control, oxygen transport, digestion, and nutrient production and absorption. They also are crucial to feelings of hunger and thirst and circadian cycles, and they even play a role in mood and emotion.

A departure from homeostasis can result in discomfort, pain or malfunction. When prolonged, it can lead to disease. But the medications that we take, or the treatments that we undergo, can also have an effect on homeostasis. It is those disruptions that can give rise to side effects. For example, a drug known as hydralazine, which relaxes blood vessels, is effective for the management of hypertension. It is believed to work by affecting calcium ion homeostasis. But the drug can also stimulate the sympathetic nervous system, which can lead to side effects such as dizziness or headache.

Another example is non-steroidal anti-inflammatories, or NSAIDs, which ease pain and inflammation. They work by reducing production of an enzyme the body uses to mount an inflammatory response. But NSAIDs also change the behavior of cells in the stomach that help maintain optimal pH levels, which can lead to tissue damage. This side effect of NSAIDs is caused by an unintended disruption of homeostasis.

How a drug affects someone, including the side effects they may experience, depends on a number of factors. These include the person’s size and weight, age, metabolism, kidney and liver function, activity level, genetic makeup and habits such as smoking or drug use. Genetics plays a role, as well. Bottom line: Our response to medications, and the side effects they may cause, are as varied and individual as the people taking them.

(Send your questions to askthedoctors@mednet.ucla.edu, or write: Ask the Doctors, c/o UCLA Health Sciences Media Relations, 10960 Wilshire Blvd., Suite 1955, Los Angeles, CA, 90024. Owing to the volume of mail, personal replies cannot be provided.)