Dear Doctor: Does insulin resistance increase as we age? I just read it has something to do with the gut. Why would that be true?

Dear Reader: To talk about insulin resistance, we should start with insulin. It’s a hormone produced by the pancreas that helps to make glucose available to the body, which uses it for energy. After you eat, as your body digests the food, glucose is released into the blood. The pancreas then releases insulin. This hormone makes it possible for muscle, fat and liver cells to absorb glucose. When your insulin metabolism is working properly, cells get the building blocks they need to produce energy, and the level of glucose in the blood remains within a healthy range.

One way things can go awry is insulin resistance. This means that even though the pancreas releases insulin into the blood, the fat, muscle and liver cells don’t respond properly to the hormone. This leaves too much glucose in the blood, which prompts the pancreas to release even more insulin. As long as the beta cells of the pancreas remain capable of producing the extra insulin that the muscle, fat and liver cells now need, blood sugar levels will remain in a healthy range. But once the pancreas can no longer keep up with the increased demand for insulin, the resulting extra blood glucose can lead to an individual developing Type 2 diabetes.

It’s estimated that up to 1 in 3 Americans, including half of people age 60 and up, experience insulin resistance. Last year, the results of a study published by scientists at the National Institute on Aging shed light on possible reasons for the link between age and insulin resistance. For answers, the researchers turned to the gut. Specifically, they became interested in the fact that despite differences in ethnicity, geographic location and the contents of their diets, people had similar changes to their gut microbiomes as they aged. One of these changes is a decrease in the healthy layer of mucus in the gut, which is needed for optimal production and absorption of nutrients. The health of this mucus layer relies, in part, on a specific beneficial bacterium known as Akkermansia muciniphila, or Akk.

While studying mice, and then rhesus monkeys, researchers found that aging was associated with a drop in levels of mucus-friendly Akk. This triggered a series of events that gave rise to certain immune cells, which were linked to insulin resistance. When levels of Akk bacteria were restored to normal, the insulin metabolism in the animals returned to normal as well.

The research is exciting because it opens up new avenues of inquiry into the problem of insulin resistance. It’s good news because Type 2 diabetes has already reached epidemic proportions around the world. Now, with a rapidly aging population, novel therapies to maintain a healthy insulin metabolism are more important than ever.

(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: Why is melanoma so dangerous? I had a squamous cell growth removed, and it was no big deal. However, a mole that had to be biopsied for melanoma (it turned out to be benign) has my doctor worried.

Dear Reader: We’re glad to hear your biopsy results came back negative for melanoma, and we can understand your doctor’s concern. Melanoma isn’t the most common skin cancer, but it is the most serious. This type of cancer can grow quickly and aggressively spread to other parts of the body. Although melanoma accounts for just 1% of all skin cancer diagnoses, it causes the majority of skin cancer deaths. Early diagnosis and treatment is crucial.

Skin cancer is the most common type of cancer, with about 9,500 new cases diagnosed each day. More people are diagnosed with skin cancer each year in the United States than all other types of cancer combined. Like all cancers, it occurs due to abnormal and uncontrolled cellular growth.

Squamous cell and basal cell carcinomas, the first- and second-most common types of skin cancer, are named after the types of skin cells from which they arise. They tend to grow slowly, and it is uncommon for them to spread. Melanoma arises from melanocytes, cells that produce a brown pigment called melanin. Researchers have discovered that unlike other cancer cells, which have to “learn” how to spread through the body, melanoma cells are equipped with a cellular mechanism that lets them start spreading immediately. That’s why this cancer is so deadly.

Risk factors for melanoma include a history of sunburn, excessive exposure to UV light, the use of tanning beds, having fair skin, a family history of the disease and having a large number of moles or certain types of unusual moles. Normal moles generally have a consistent color -- usually tan or brown -- and uniform borders. When moles change shape or color, become irregular, get crusty or bleed or grow larger, or when new moles or skin discolorations appear and change, it can be cause for concern. A mole that looks markedly different from the other moles on your body can also indicate something is wrong. These warning signs have been turned into a memory prompt, the “ABCDE rule”:

-- Asymmetry: The halves of a mole or birthmark don’t match.

-- Border: Edges are irregular, jagged or blurred.

-- Color: Color is irregular or patchy, sometimes with areas of red, pink, white or blue.

-- Diameter: Moles larger than 1/4 inch across, although melanomas can be smaller than that.

-- Evolving: A mole or birthmark that begins to change shape, color or size.

Studies show that regular sunscreen use can cut melanoma risk in half. Considering that the number of melanoma deaths is expected to increase by 22% in 2019, this bit of self-care can be a life-saver. Note and keep a record of the moles on your body and how they change. If you see any of the ABCDE characteristics, contact your doctor immediately.

(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.)

Hello again, dear readers, and welcome to the oh-yes-it’s-summer edition of our monthly letters column. To date, it seems no part of the nation has escaped the unique misery of a heat wave. Please be careful when temperatures spike, and take all local heat advisories seriously. It’s easy to underestimate the effects of extreme heat and humidity and to overestimate our ability to withstand it. Limit outdoor or strenuous activities, particularly during the peak hours of 10 a.m. to 4 p.m. Use air conditioners or fans if you have them; if not, take refuge in an air-conditioned mall or a cooling center. Drink plenty of water and avoid alcohol. Check in with children and the aged, who are particularly susceptible to heat exhaustion and heat stroke.

And now, your letters. We recently answered questions about a study that found the sustained scent of a tempting food had the unexpected effect of actually easing the craving for a snack. Several of you wrote to say you’ve experienced this phenomenon, including a reader from Grand Island, Nebraska. After two years of working in an ice cream shop, she developed an aversion to the sweet treats she was working with. “Now, 40 years later, I finally like small servings of ice cream occasionally, but no gooey toppings -- ever!” she wrote. “I would joke that the perfect diet would require me to work full time for two years each for a bakery, a pizza parlor, a steakhouse, etc. Aversion therapy does work! Ice cream may not have much aroma, but the sensory overload did the trick!”

A column about the fairly new idea of creating an advanced care directive specific to a dementia diagnosis rang true for many of you, who said it prompted important conversations and even some decision-making. We heard from a paramedic in Terre Haute, Indiana, who asked families and caregivers to honor the advanced care directives of their loved ones. “Too many times I have been called on a respiratory/cardiac arrest, and when I ask if the patient has a DNR (do not resuscitate) or advanced directive, there is one person who says, ‘Yes, she has a DNR, but I'm revoking it. Save her!’“ he wrote. “I understand that sudden death can cause people to act contrary to people’s wishes. However, if a person has taken the time to have their wishes properly documented, family members and caregivers need to understand that this is what the patient wants.”

We continue to hear from older readers about their pets and the companionship, joy and sense of purpose they bring. An 87-year-old reader in Simi Valley, California, says her two small dogs get her out of the house for a walk several times a day. “The exercise keeps my legs moving so I don’t end up in a wheelchair,” she wrote.

Thank you, as ever, for taking the time to write to us. We look forward to hearing from you, and will see you back here next month.

(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.)