Dear Doctor: It seems like doctors always want to schedule surgeries as early as possible. But I recently read that heart surgery survival chances are better in the afternoon. Why would this be? Should people push their doctors for afternoon surgeries?

Dear Reader: You're referring to the results of a study published in the journal Lancet last month. Over the course of six years, scientists from the University of Lille in France examined the medical data of close to 600 patients who underwent a heart surgery known as aortic valve replacement. In this surgery, the aortic valve, which regulates blood flow to the heart, is replaced with either animal or synthetic tissue. What the researchers wanted to know was whether the time of day that these surgeries took place played a role in which patients went on to experience serious complications.

The results were surprising. Researchers found that patients whose surgeries were performed after noon had half the risk of heart attack, acute heart failure or death in the 500 days after surgery than did those whose procedures took place in the morning. A separate analysis of 44 patients who had morning surgery, and 44 who had afternoon surgery, examined the rate of a certain type of tissue injury that can occur when the patients are taken off bypass during the operation and blood flow returns to the repaired structures of the heart. Once again, the patients with afternoon surgeries fared measurably better than those with morning surgeries.

These findings seem to add to a growing body of evidence that circadian rhythms -- that is, our biological clocks -- have an effect on health care interventions. Previous studies in mice have suggested that the body responds best to chemotherapy during certain times of day. A large-scale study into flu shots found that, among older people, those who received the vaccine in the morning produced more antibodies than those who got an afternoon injection.

Ongoing research continues to show that circadian rhythms play a role in all aspects of physical and mental health. Here at UCLA, scientists are looking into the connection between chronic disruption of circadian rhythms, as in workers on swing or night shifts, and the increased risk of developing diabetes and metabolic syndrome. Previous research has shown that circadian disruption affects learning, mental and emotional health, and can even lead to death. This line of inquiry is considered to be so important that last year the Nobel Prize in Medicine went to three researchers who identified the molecular mechanisms that control our body clocks.

That said, there are certain caveats regarding this new heart surgery study. As an analysis by the National Institutes of Health notes, 600 patients make a small sample size. Each of these patients was treated at the same hospital, which begs the question whether it was the time of day of the surgeries, or the specific surgical teams that performed them, that had the greatest effect on the outcomes.

We need additional studies in multiple medical sites, and with a diversity of heart procedures, before we can conclusively link time of day to better surgical outcomes.

(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: How is one screened for/diagnosed with Alzheimer's or other forms of dementia? What type of doctors does one see? What sorts of tests do they run? It runs in my family, and lately I've been forgetting conversations soon after they happen. But I don't know where to look for answers.

Dear Reader: Your concern is understandable. The degeneration of the brain's ability to incorporate new information -- and the loss of the hardwiring that controls our everyday tasks -- affect not only an individual but everyone who cares for that person as well. Further, the genetic linkage is greatest for people with a parent or sibling who developed dementia prior to the age of 65. (The linkage grows progressively weaker with the family member's age of diagnosis, so much so that if the person was diagnosed after 85, one's own risk is no different than if there were no family history.)

Further, the rates of dementia are increasing in this country, with Alzheimer's dementia affecting 5.4 million people in the United States in 2016. Some of this may be due to our ability to diagnose the disease, but our increasing rates of risk factors -- diabetes, obesity and lack of physical activity -- play a role as well. The majority of people are diagnosed after the age of 65, with the overall incidence of dementia doubling every 10 years after the age of 60.

Diagnosis typically starts with your primary care doctor. While blood tests can pick up some non-Alzheimer's causes for memory loss, such as B12 deficiency, the standard screening exam is the Mini-Mental Status Examination (MMSE), a memory and writing test. That said, another test, the Montreal Cognitive Assessment (MoCA), has greater sensitivity in identifying losses in the abilities to use language and perform tasks -- both common markers for encroaching dementia -- so your doctor may use this as well.

These tests can effectively identify people who already have dementia, but they are less effective at identifying people in the early stages of memory loss or those who have memory loss but also have a higher level of brain function. In these cases, much longer and more formal neuropsychological tests may be necessary. This testing is often done by a psychologist associated with a neurologist.

A neurologist may also order imaging tests of the brain. These tests can include an MRI, positron emission tomography (a PET scan) and possibly functional brain imaging that assesses areas of the brain with low activity. Although some findings might suggest Alzheimer's, these tests are used primarily to rule out other causes; they can't yield a definitive Alzheimer's diagnosis.

The potential to use cerebrospinal fluid biomarkers to help diagnose Alzheimer's disease is still in the investigational phase and unlikely to be used by a neurologist currently.

So start by talking to your primary care doctor about the change in your memory, how long it's been happening and whether it's rapidly getting worse. Your doctor will likely conduct a standardized test for memory, along with blood work to rule out other causes of memory loss. If that suggests a problem, but no other physical cause, you should see a neurologist for more formal testing.

(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 read that grandparents can increase a child's cancer risk by encouraging bad behaviors. Quite frankly, I'm offended by this. Couldn't they also improve a child's health? When our grandkids are visiting, we get them to eat much healthier food than they typically get at home.

Dear Reader: We confess that we cringed a bit as we read some of the headlines that the study you are referencing has generated. A very important message -- the rules of health and nutrition hold true no matter who is breaking them -- is getting buried beneath needless snark.

To answer your question: Yes, by offering the right nutritional guidance and making wise food choices, grandparents can absolutely have a positive effect on a child's health. We're happy to hear that you focus on a healthful diet when your grandkids are around, but suspect you are far from alone in this endeavor.

So how did this "grandparents may be bad for kids' health" conversation get started?

Researchers from the University of Glasgow in Scotland were interested in learning what role, if any, additional caregivers may have on the risk factors for non-communicable diseases in children. In the majority of cases, these secondary caregivers were grandparents.

The researchers noted that the positive habits and behaviors that can help avert up to 40 percent of the cancers that develop in adulthood are actually acquired in early childhood. These include sticking to a healthful diet, getting regular exercise, not using tobacco products, not abusing alcohol, limiting or mitigating sun exposure, and avoiding excess weight gain.

The question then became what sort of effect the grandparents' approach to those positive behaviors had on the children's cancer risk. To that end, researchers analyzed data collected in 56 studies that had been conducted in 18 different countries.

This new study, which was published last November in the journal PLOS One, found that the primary risky behavior that grandparents took part in was overfeeding their grandchildren. That is, the grandparents took a more indulgent approach to their grandchildren's diets. They offered them more treats than their parents did and provided larger portions during meals. This meant the kids were eating too many calories, many of them coming from sugar, fat and processed foods. This resulted in the grandchildren gaining weight.

Another factor was activity levels, which were lower among children when being cared for by grandparents than when they were with their parents. In some cases, the children were exposed to tobacco products and secondhand smoke in their grandparents' homes. The upshot of all these behaviors was a measurable increase in the risk factors that can lead to heart disease, diabetes and even cancer later in life.

One thing the researchers were careful to address, and which didn't appear in the stories we read, was why this was happening. In some countries, excess weight was a cultural sign of health and prosperity. For some grandparents who had been raised in wartime or in poverty, abundant food was a symbol of safety and stability.

Rather than being uncaring or careless, many of the grandparents in the study believed they were helping the children.

(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.)