Dear Doctor: I read about a study that said smelling junk food you want to quit eating -- hello, pizza and donuts! -- will stop your craving. Is that really true? I want to eat healthier, but some foods are so hard to resist.

Dear Reader: This particular theory hadn’t crossed our radar until we read your letter, but we did a bit of digging and found the study you’re referring to. It was conducted by researchers at the University of South Florida and published at the start of the year in the Journal of Marketing Research.

The study's findings were as you say -- the sustained scent of a tempting snack food had the effect of easing the craving for that snack. That’s somewhat ironic, considering the point of the study was to examine more closely the practice of using ambient scent in public settings as a marketing ploy.

These ambient scents are part of an increasingly common practice in which retailers infuse areas with seductive smells to act as "aroma billboards," as one advertising company put it, to drive food sales. Anyone within sniffing distance of a Cinnabon stand in a mall has directly experienced this technique. Stories about the practice mention chocolate-scented strips placed on vending machines in California that caused the sales of Hershey bars to triple, a grocery store in New York whose bakery sales spiked whenever the scent of fresh-baked bread was pumped through the aisles, and the use of a variety of hidden scent machines throughout Disney properties to encourage spending. The practice is used in nonfood-related marketing, too, with a variety of pleasant scents used to make shoppers subliminally happy in order to loosen their purse strings.

According to the study you asked about, it turns out there’s an important catch when it comes to the scent-driven marketing of food: The researchers found that whether or not a scent triggered a craving was directly related to the amount of time someone spent smelling it. The tests were conducted in several sites, including a grocery store and a middle school cafeteria.

Researchers used a hidden nebulizer, which is a device that broadcasts scent. Individuals were exposed to alternating pairs of scents, one of a healthful food, and one of a junk food item. The scent of strawberries was paired with the aroma of chocolate chip cookies, and the scent of apples was paired with that of pizza. A quick whiff of a cookie -- 30 seconds or less -- often led to the cookie being selected rather than the strawberry. But when the cookie scent lingered for 2 minutes or more, the cookie lost its allure, and participants chose to eat the strawberry instead. The apple-pizza combo had the same time-dependent results. The takeaway is that by inhaling the scent of a tempting food long enough, you’ll move past craving it and arrive at the point where the scent itself has satisfied the craving.

A final word -- this was a single experiment on a complex subject, and scientists, including the researchers, agree further study is needed to fully understand the results.

(Send your questions to askthedoctors@mednet.ucla.edu, or write: Ask the Doctors, c/o UCLA Health Sciences Media Relations, 10880 Wilshire Blvd., Suite 1450, Los Angeles, CA, 90024. Owing to the volume of mail, personal replies cannot be provided.)

Dear Doctor: I read that a girl went blind in one eye after playing video games on her phone for an entire day. Is this even possible? Should I be worried about my kids, who are video game addicts?

Dear Reader: You’re referring to a news story from China that made headlines a few years ago. The woman in question, who was 21 at the time, reportedly spent an entire day playing an online video game and suddenly lost the vision in her right eye.

Doctors diagnosed her with retinal artery occlusion, a blockage in the main vessel that supplies blood to the retina. The retina is the layer of light-sensitive tissues at the back of the eye that translate the energy from incoming light into impulses. These impulses then travel via the optic nerve to the brain, where they are interpreted as visual images.

When the retinal artery becomes blocked, oxygen-rich blood can’t reach the retina. This can result in cell death and vision loss. The speed at which the cells of the retina die and the extent of the damage depends on the degree of arterial blockage and how long it lasts.

Retinal artery occlusion usually occurs in people 60 and older, and it is slightly more common in men. The cause of the blockage is usually a blood clot or an embolus, which is a bit of foreign matter in the bloodstream, such as an air bubble or a bit of fatty deposit. Risk factors for the condition include high blood pressure, diabetes, heart arrhythmias, carotid artery disease, the use of oral contraceptives, faulty heart valves and blood platelet abnormalities, to name just a few. It is not known which specific risk factors applied to the woman in the story.

At this time, there are no reliable treatments for retinal artery occlusion. Most involve procedures to somehow dilate the affected artery, dislodge the blockage and restore normal blood flow.

Regarding the claim that the young woman’s marathon gaming session caused the arterial blockage, there turns out to be a bit more to the story. With an estimated 2.3 billion-with-a-B people worldwide regularly playing online games, addiction has become a serious concern. In China, authorities have identified online gaming addiction as a public health crisis. Stories of gamers forgetting to eat, skipping school, getting fired from work and even wearing disposable diapers in the pursuit of their online gaming passions abound.

The patient in the news story had been playing a hugely popular game known as Honor of Kings. The parent company claims to have more than 80 million daily active users, and 200 million players per month. Some observers believe that, despite the lack of an established medical connection between extreme eye strain and retinal artery occlusion, authorities have used the patient’s medical emergency as a vivid cautionary tale to fellow gamers.

When it comes to your own kids, it’s highly unlikely that their gaming habits will physically blind them. However, any time a single activity takes precedence over daily activities and other life interests, we believe there is cause for concern.

(Send your questions to askthedoctors@mednet.ucla.edu, or write: Ask the Doctors, c/o UCLA Health Sciences Media Relations, 10880 Wilshire Blvd., Suite 1450, Los Angeles, CA, 90024. Owing to the volume of mail, personal replies cannot be provided.)

Dear Doctor: I recently read about advance directives that deal only with dementia. Is there some benefit to those over the more traditional directives? If so, how do I go about creating one?

Dear Reader: Most of us are probably familiar with the concept of the advance health care directive, which is sometimes referred to as a living will. It’s a legal document that outlines your specific wishes regarding medical and health care decisions, including end-of-life care, in the event that you are unable to do so.

But with the number of people living with dementia expected to nearly triple worldwide by 2050, some in the medical community now see a need to expand the scope of the advance directive. This was formally addressed in an opinion piece in the December 2017 issue of the Journal of the American Medical Association, where the authors made a case for crafting an advance directive specifically for dementia.

Their thinking is that because dementia is a disease that progresses in stages, a person’s health care goals should similarly follow a gradual trajectory. Cognitive decline often occurs over the course of years or even decades. That means that standard advance health care directives, which dictate decision-making in times of crisis, aren’t always the right fit. With a dementia-specific advance directive, the individual addresses a range of questions based on how cognitive decline typically progresses. Not only does this allow them to make specific choices regarding health care and quality of life, it frees family members from difficult decisions and painful arguments. This includes decisions about undergoing a range of medical tests, medical care and end-of-life interventions.

The dementia-specific advance directive proposed by the authors of the JAMA essay divides cognitive decline into three phases -- mild, moderate and severe. The individual indicates his or her health care goals for each phase of dementia.

These goals are further broken into four stages. The first stage is living as long as possible, which includes accepting all medical interventions, including restarting the heart should it stop beating. The second stage is to receive certain types of medical care but to decline efforts to restart the heart. The third stage indicates a person’s wishes to receive limited medical care, and only in the place where they are living, not in a hospital. The final stage is a request for palliative care, which means addressing only the comfort of the patient, with no efforts to prolong life.

Questions about treatment like antibiotics, the placement of a pacemaker, the use of dialysis, blood transfusions, respirators or feeding tubes can all be addressed within the framework of the document. The authors stress that this type of advance directive must be filled out before any signs of dementia have presented themselves, and the document should be revisited regularly for amendments and updates.

As with all advance directives, it’s important to have these documents drafted by an attorney so they will be legal in the individual’s state. And it’s vital to have copies readily available for when they are needed.

To learn more, or to create your own document, visit dementia-directive.org.

(Send your questions to askthedoctors@mednet.ucla.edu, or write: Ask the Doctors, c/o UCLA Health Sciences Media Relations, 10880 Wilshire Blvd., Suite 1450, Los Angeles, CA, 90024. Owing to the volume of mail, personal replies cannot be provided.)