Dear Doctor: I recently read that marriage reduces the risk of mental decline in old age. I'm not sure I buy it. But, assuming it's true, why would that be?

Dear Reader: You're likely referring to a recent study in the journal Neurology, Neurosurgery and Psychiatry that combined data from 15 studies with a total of 812,047 people. In each of the studies, the authors looked at the marital status of participants over age 65 and the overall rate of dementia. Most of the studies were performed in Europe, with the largest -- 750,129 participants -- conducted in Sweden. The average age of all participants was 73 years.

The data did suggest a protective effect from marriage, with lifelong single people having a 42 percent higher risk of dementia than married people, and widowed people having a 20 percent higher risk. The researchers found no differences based on gender.

Interestingly enough, in the primary analysis, divorced individuals had the same rates of dementia as their married counterparts. But, notably, when researchers looked at data from the large Swedish study, they found twice the risk of dementia among divorced people who began the study between the ages 50 and 64 and 1.4 times the risk among divorced people ages 64 to 75.

There's no one good explanation why marriage would benefit brain function. It may be that marriage challenges a person. In the needed conversation between the partners in marriage, there are differences of opinion, a necessity for mental flexibility, and a level of stress that requires people to go outside of their comfort zones and challenge their brains. It also may be that married life leads to social interactions with other couples or with in-laws, which lead to greater human interaction -- even if all of them aren't pleasant.

Obviously, marriage tends to provide greater social support. To know that somebody cares about you can reduce depression and anxiety, which also may lead to a greater desire to take care of yourself both physically and mentally. This self-care, in turn, may help ward off dementia. That could be why being widowed is associated with a greater risk of dementia, compared to being married.

Then there are the health aspects of marriage. Other studies have found that marriage is linked to increased longevity, which suggests that dementia risk may be reduced through a decreased rate of illnesses and habits that can increase the likelihood of dementia.

Ultimately, although marriage may provide a modest benefit in warding off dementia, I would look at this data with a grain of salt. Many people who have never been married, who have been divorced or who are widowed obviously lead long lives without any trace of dementia. Certainly, no one would recommend an unhappy marriage as a possible protective factor against dementia risk.

Further, the recently published data are from older individuals. The study's ultimate conclusion may be applicable to a different world than the one in which we currently live. In this day and age, society is more accepting of a single life; our current world may be stimulating and protective enough on its own.

(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: We just got a new puppy, but I'm almost afraid to let my child play with it. I read a news story that said puppies have been linked to some sort of bacterial infection. What should I do?

Dear Reader: The news you're referring to is the outbreak of campylobacteriosis, an infectious disease linked to puppies purchased from Petland, a national chain of pet stores. Campylobacter bacteria is one of the most common sources of diarrheal illness in the United States. Although campylobacteriosis is most often associated with raw or undercooked meats, the bacterium can be present in the feces of dogs and cats as well.

What made this particular outbreak problematic was that the bacteria involved proved to be resistant to the first-line antibiotics that are most commonly recommended. This type of resistance is associated with an increased risk of hospitalization, the development of a bloodstream infection, or in extreme cases, treatment failure in patients.

The outbreak, which began in September 2017, eventually spread to 17 states. As of mid-December, laboratory tests confirmed illness in 97 people linked to this outbreak. And as of this writing, about 25 percent of them were hospitalized. No deaths had been reported.

If your puppy came from a Petland store (there are about 80 nationwide), you should contact the company. As requested by the Centers for Disease Control and Prevention, which tracks these types of outbreaks, Petland will help you to determine whether your puppy is likely to have been infected.

The truth is that virtually every living creature, humans included, is a carrier of something that can be transmitted to the people (and animals) around them. While there is growing evidence that repeated contact with pets and farm animals can help to build up the immune system, it's important to be aware that potentially dangerous organisms can be transmitted as well.

Psittacosis, a respiratory infection caused by a bacterium, is sometimes seen among owners of pet birds, like parrots and cockatiels, and in poultry, like turkeys or ducks. The Toxoplasma parasite, sometimes found in cat feces, has an estimated 30 million carriers in the U.S. alone. (Most have no symptoms thanks to the immune system.) Roundworm, a parasite that at some point infects most dogs, particularly puppies, can also be transmitted to humans.

The point here isn't to alarm but rather to encourage good pet hygiene. With just a few easy steps, you can keep your family safe and go on to enjoy the multitude of benefits afforded by having a dog in your life.

-- Be meticulous about keeping your yard cleared of dog feces, picking it up as soon as possible.

-- Avoid physical contact with feces and urine by wearing gloves or using a sturdy pooper scooper while cleaning up.

-- When discarding feces into the trash, put it into an impermeable bag and tie it off.

-- Wash your hands when you're finished with scooping duties and after extended physical contact with your pet.

Finally, for your puppy's safety as well as your own, take him for regular veterinary visits, have his stool checked as needed, and make sure he's up to date on vaccinations.

(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 have aplastic anemia. It is hard to explain this to people. Most of them hear the anemia part and get stuck there. I hear often: "Just take some iron" or, "My aunt had that and was cured with B12 shots." How do I quickly explain it better?

Dear Reader: How frustrating this must be for you. To put it simply for people, you could say that aplastic anemia is a bone marrow disease that leads to bone marrow failure. If they stare at you glassy-eyed, you might want to leave it at that, but if they're truly interested, you can try a longer explanation.

Start by saying that aplastic anemia is a rare disorder, diagnosed in one in every 500,000 people per year. The incidence is two to three times higher in Asia. Then you can explain that the function of the bone marrow is to produce red blood cells, white blood cells and clotting cells called platelets. The bone marrow contains specific cells, called hematopoietic stem cells, that are necessary to produce all of these. With aplastic anemia, these stem cells are damaged, so all of the cell lines are diminished.

Most cases of aplastic anemia are due to an attack by the body's immune system on the bone marrow, which destroys the hematopoietic stem cells. The cause of this attack is unknown, but a virus, chemical, drug or mutation may be the instigator, altering the immunity so that the white blood cells see the stem cells as foreign and thus attack them.

As the name implies, the disease causes anemia, which is a lowering of the red blood cell count. This can lead to significant fatigue and stress on the heart, which has to pump this deficient blood to the rest of the body. In addition, depletion of the white blood cells leads to an increased risk of pneumonia, urinary tract infections and severe bloodstream infections. When the white blood cell counts are chronically low, patients face a risk of invasive fungal infections, which can lead to death. Further, the lowering of the platelet counts increases the risk of bleeding due to the blood's decreased clotting ability. Ultimately, mutations in the bone marrow can lead to leukemia.

Aplastic anemia treatment depends upon the severity of the disease, the patient's age and whether the patient has other illnesses. You might want to explain that, because of the disease's potential complications, treatment is much more aggressive than taking iron or B12 supplements.

In fact, the treatment with the greatest chance of success is the transplantation of hematopoietic stem cells from a donor -- a difficult treatment with severe side effects. And although transplantation can lead to prolonged survival, it also often fails. This approach, which requires a compatible donor, is recommended for healthier patients and those younger than 50. Another method of treatment is the suppression of the immune system's attack on the cells in the bone marrow. This requires a combination of medications, which can also have significant side effects.

Maybe this explanation will help people understand the severity of aplastic anemia and to be more understanding of what you are going through. If not, at least be assured that some people do understand your battle -- and wish you strength and recovery.

(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.)