Dear Doctor: Does outlook really matter when it comes to lifespan, as a recent study suggested? I'm not a wet blanket, but I don't have a relentlessly sunny disposition either.

Dear Reader: Let's say it's a gray, cloudy Monday morning. You're stuck in traffic, listening to the news of another atrocity in some distant land. Such a scenario would not in itself arouse feelings of optimism. Instead, an optimistic person might focus on feeling excited about his or her job, realize that the traffic is going to get better, and take solace in the fact that humanitarian efforts will be made to stop further atrocities.

In my own experience, I've seen pessimistic, unhappy people lead very long lives, and I've seen optimistic people's lives cut short by illness. That doesn't mean that, in the aggregate, optimism has no effect on lifespan.

Specific studies have looked for correlations between an optimistic outlook and cardiovascular disease, finding mortality benefits among those who had a more optimistic attitude. These studies used different scales to judge a person's level of optimism, with one common approach using a questionnaire about a person's approach to life. Some, for example, asked people to respond in either agreement or disagreement to statements such as, "Overall, I expect more good things to happen than bad."

A combined evaluation of many studies assessing the connection between optimism and physical health was reported in the Annals of Behavioral Medicine in 2009. Researchers measured physical health outcomes by rates of cancer, heart disease, infection rates, pain, diabetes and kidney failure. In the combined evaluation, the authors found a small correlation between better physical health and optimism, and an even smaller correlation between lower death rates and optimism.

A more recent study published in 2016 in the American Journal of Epidemiology followed 70,000 nurses and judged levels of optimism by how they responded to a questionnaire called the Life Orientation test. The women responded to 10 different statements such as, "In uncertain times, I usually expect the best," "I rarely count on good things happening to me," and "I'm always optimistic about my future."

The researchers ranked women into four quartiles, from lowest to highest, and found that those who were most optimistic had a 26 percent decrease in the death rate over the study period compared to those who were the least optimistic. This was after adjusting for depression, because some people who aren't optimistic may actually be depressed. The decrease in death rates was seen for deaths caused by cancer, strokes, heart attacks and infections.

One problem with the study is that women who were the most optimistic had lower smoking rates, were more physically active, had more education and were more likely to be married. Each of these factors is associated with greater longevity. The authors say they adjusted for these factors, but fully adjusting for them is difficult. Another problem with the study is that the study might not reflect correlations within the general population, in that 97 percent of the women identified themselves as white.

Overall, the study found what appears to be a correlation between optimism and a better cholesterol level, higher blood levels of antioxidants and improvements in one's immune system.

My own feeling is that optimism is less about sunniness than about hopefulness. This hopefulness helps people get through the bad times, because they realize that good times are ahead. And, overall, such people seem to have healthier habits that can help lead to greater longevity.

(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: I had toenail fungus two years ago, and my doctor prescribed Lamisil. It took a long time, but it worked. Now the fungus, which is so ugly, is back again. Why is it so hard to get rid of, and are there any new treatments available?

Dear Reader: Toenail fungus is fairly common, but that's not much consolation to the 6 million or so people in the United States who have to put up with it. It's an often-unsightly infection caused by a microscopic organism called a dermatophyte that lives beneath the toenail. More precisely, it colonizes the portion of the nail known as the matrix, which is underneath the cuticle.

Initial symptoms are a yellowish or brownish discoloration of the toenail. As the infection progresses, nails will often become thickened, crumbly and malformed. Although the fungus affects the appearance of the nails, it actually lives on the layer directly beneath the toenail. That's why it's so difficult to treat.

Your nails are made up of keratin, a tough, fibrous protein. The same hard shell that protects your toes is giving shelter to the fungus. For topical medications to be successful in killing the fungus, they have to be able to reach it.

Anti-fungal creams and liquids are available, both in over-the-counter preparations and by prescription. But because nails are not porous, it's difficult for the medication to reach the infection in concentrations great enough to kill the fungus. As a result, success rates for topical treatments are low.

Systemic medications, like the Lamisil your physician prescribed, take a more direct approach. You swallow the pill, it gets digested, and the medication enters your bloodstream. Your circulatory system delivers the medication directly to the fungus living beneath your toenail and, in the best-case scenario, kills it.

However, there are drawbacks. Side effects can include headache, nausea and diarrhea. In rare cases, the drug can cause liver damage, so blood tests to monitor potential toxicity are needed. These infections are quite persistent, and your experience with recurrence is fairly typical. Although oral medications are the most effective, reported failure rates are as high as 20 to 30 percent.

Nail growth is slow, which means treatment is a lengthy process. A big toenail can take anywhere from a year to 18 months for new growth to completely replace the old, infected nail. Oral treatment for toenail fungus generally lasts 12 weeks. Topical preparations must be applied for at least a year.

Nail fungus is not a health risk to most people. But anyone with a compromised immune system, such as a diabetic who contracts nail fungus, is at risk of developing serious complications like foot ulcers. Therefore, it's vital that diabetics seek medical treatment.

As for your question about new treatments, some physicians and podiatrists offer laser treatment of toenail fungus. Although some patients report good results, reliable data about the long-term efficacy of laser treatment is scarce.

Our recommendation is that you meet with your primary care physician, who will want to do a physical exam of the affected area. Then you can discuss the specifics of the recurrence and evaluate which of the existing treatments are best for you at this time.

(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: Will eating nuts really reduce my risk of heart disease, cancer and other diseases, which a new study has suggested? If so, how many should I be eating?

Dear Reader: Nuts are fruits. They consist of a hard shell and an edible seed. To answer your question, I'll use the definition of nuts to refer to the varieties we typically eat, although some, like the peanut, are not truly nuts. Nuts are a good source of fiber and contain antioxidants such as vitamin E, healthy polyunsaturated fats and magnesium. These aspects of nuts could reduce the risk of vascular disease and cancer and possibly rates of diabetes.

A 2013 study published in the New England Journal of Medicine looked at nut intake per week among both male and female health professionals. The researchers followed 173,000 people for a period of 30 years and looked at how many of those people died. They found a marked decrease in death rates among those study participants who ate nuts. They also found that the benefit was dose-dependent, meaning that the more nuts people ate per week, the smaller their chance of death during the study period. Compared to people who rarely ate nuts, those who ate nuts once per week had an 11 percent decrease in death rate, while those who ate nuts daily had a 20 percent decrease in death rate.

A much larger recent study, published in the journal BMC Medicine, combined multiple studies and looked at rates of death from heart attacks, strokes and cancer. The studies were from the United States, Europe, Asia and Australia and included a total of more than 819,000 participants. The study quantified the benefits of nuts by the number of servings per day.

The study authors found a 19 percent decrease in death rates among people who were high nut consumers compared to people who were low nut consumers, with a 24 percent decrease in heart disease, an 11 percent decrease in stroke and an 18 percent decrease in cancer. The authors also found that the greatest benefit was seen among those who consumed at least 15 grams to 20 grams of nuts five or six days per week. These results appear to support the findings in the New England Journal study.

So how many nuts is 15 to 20 grams? About 14 almonds, four Brazil nuts, 11 cashews, 12 hazelnuts, nine walnut halves, 29 pistachios and 18 peanuts.

That's not a lot. I'm not suggesting that you precisely count the number of nuts that you eat at any given time, but I would suggest that you eat nuts frequently, perhaps as a snack. I have them on my desk at work. They're much better for you than the unhealthy, high-sugar, high-carbohydrate snacks that can lead to obesity, diabetes and higher death rates. Nuts are high-energy snacks that provide a more sustained suppression of hunger than sugary snacks.

If you don't eat nuts already, start slowly. You may like some more than others, and you may tolerate some better than others. In any case, have some nuts; they're good for you.

(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.)