Dear Doctors: What are microplastics, and where do they come from? They’re all over the news, and it’s hard to tell if they’re a real problem or just another internet scare. One news story said there’s an entire teaspoonful of microplastics in our brains. Is this true?

Dear Reader: We suspect the recent increase in headlines about microplastics is due to emerging research that finds these miniscule pollutants to be far more widespread and abundant than was previously known. The focus reflects growing concern about the harmful effects of microplastics on the physical health of humans and other living things, and on the environment.

Microplastics are just as they sound -- minute fragments of plastic. The largest measure a few millimeters, smaller than a grain of sand. The smallest, a subcategory known as nanoplastics, are just a few nanometers wide. As a point of reference, the width of a human hair is about 80,000 nanometers.

Despite their tiny size, microplastics can produce adverse health effects. These include inflammation and oxidative stress, and possible links to heart and circulatory problems, autoimmune disorders, certain cancers and reproductive problems in both women and men.

As for where microplastics come from, it’s almost easier to talk about where they are not found. Manufacturers use microplastics in products as varied as cosmetics, fabrics, household cleaners, building materials, furniture, clothing, sunscreen, pesticides, food containers, water and beverage bottles, paint, decor, personal care products and medications. These are known as primary microplastics. They are also generated through the breakdown of products that are made from or contain plastic -- known as secondary microplastics.

Recent studies have found secondary microplastics in virtually every part of our environment. They are in the soil and in the air, in streams, rivers, lakes, the ocean and in the bodies of the creatures that live in those habitats. Microplastics are present in whole and processed foods, and throughout our bodies.

A study by researchers at the University of New Mexico, published earlier this year in the journal Nature, found that accumulations of microplastics in the human body -- and particularly in the tissues of the brain -- have spiked since 2016. The researchers also found higher concentrations in the brains of individuals diagnosed with dementia. While concerning, it is important to note that causation has not been proven.

Going back to your questions, the claim that our brains contain a teaspoonful of microplastics is drawn from that study. However, it is a bit of a misunderstanding.

The researchers found that an adult human brain may contain up to 7 grams of microplastics. They equated this to the weight of a disposable plastic spoon. They were not referring to the teaspoon as a measure of volume. Still, the presence of any amount of plastic in the delicate and complex tissues of the brain is worrisome, so the correction isn’t very reassuring.

Yours is one of several letters we have received on the topic of microplastics. Our next column will explore what is known about their health effects, as well as strategies to limit exposure.

(Send your questions to askthedoctors@mednet.ucla.edu, or write: Ask the Doctors, c/o UCLA Health Sciences Media Relations, 10960 Wilshire Blvd., Suite 1955, Los Angeles, CA, 90024. Owing to the volume of mail, personal replies cannot be provided.)

Dear Doctors: I had an episode where it felt like my left eye went out of alignment and I couldn’t focus. A brain scan was clear, but the doctor said it’s cranial nerve palsy. He says it’s from a concussion I had last spring. I’m fine again but really worried. Will it happen again? Is there a treatment?

Dear Reader: You have been diagnosed with a condition known as cranial nerve IV palsy. It causes weakness or paralysis of the nerve that animates the muscle responsible for moving the eye downward and inward toward the nose. The Roman numeral in the name refers to the fourth cranial nerve, also known as the trochlear nerve. The word "palsy" indicates limited or impaired movement. The medical term for this condition is trochlear nerve palsy.

To understand what is going on, we should begin with a bit of anatomy. The human body has 12 cranial nerves, each with a distinct function. The third, fourth and sixth cranial nerves control the six muscles involved in eye movement. For the fourth cranial nerve, that’s the superior oblique muscle. In addition to moving the eye downward and inward toward the nose, the superior oblique muscle plays a role in moving the eye outward. Damage to the fourth cranial nerve can interfere with the impulses it carries to the superior oblique muscle. This can lead to significant vision impairment, including the symptoms you have described.

Trochlear nerve palsy can be congenital, which means it is present at birth. It can also be acquired, which means it occurs due to injury. Although the trochlear nerve is the shortest of the 12 cranial nerves, it takes the longest path through the skull. This leaves it uniquely vulnerable to injury, particularly when there is head trauma. That is why your doctor has drawn a connection between a concussion you suffered recently and the onset of this condition.

Symptoms include the sensation of misalignment and the inability to focus as you described. Many people experience double vision, which can be worse at night. Additional symptoms include dizziness when looking down, a need to tilt the head to keep things in focus and crossed eyes. Diagnosis is based on symptoms and a vision test, and treatment depends on the cause of the condition.

It is possible that you will have another episode. However, the good news is that when trochlear nerve palsy results from an injury, it often resolves on its own, typically in six to eight months. During the period of watchful waiting, you might be prescribed specially crafted eyewear, known as prism glasses. They have wedge-shaped lenses that bend the light before it reaches the eye. This improves vision by adjusting the misalignment caused by the malfunctioning muscles. Prism glasses are calibrated to the specific needs of each person through a vision test. If they don’t help, an eye patch may be needed. After eight months, if the condition has not improved, surgery to realign the eyes becomes an option.

(Send your questions to askthedoctors@mednet.ucla.edu, or write: Ask the Doctors, c/o UCLA Health Sciences Media Relations, 10960 Wilshire Blvd., Suite 1955, Los Angeles, CA, 90024. Owing to the volume of mail, personal replies cannot be provided.)

Kansas City, MO 64106; 816-581-7500

Dear Doctors: I recently watched a video on the positive effects of napping in regard to heart disease. I am 66; I am a lifelong athlete with normal blood pressure and an LDL cholesterol level that is slightly elevated. I’ve been considering a statin and now wonder how napping may affect that decision.

Dear Reader: The physical benefits of a nap are woven into humankind’s earliest history. Medical texts uncovered in ancient China cite napping as a way to restore balance to the body. In Hellenic Greece and ancient Rome, an afternoon nap was an important health practice. Modern-day researchers are also taking a keen interest in the effects of a daytime snooze. After more than four decades of inquiry, though, the conclusions are mixed.

Some studies, such as those referred to in the video you shared with us, found that napping can have a beneficial effect on cardiovascular health. Others have linked the practice to certain health risks. The reason for these contradictions lies in the complexities of sleep patterns and cardiovascular conditions, and the mechanisms of the studies themselves.

Let’s start with the specific research you are asking about. A study in Switzerland looked at health data from 3,500 adults. The study found that people who napped once or twice a week had a 48% lower risk of cardiovascular disease than those who didn’t nap. Another study, from researchers in Greece and the Harvard School of Public Health, analyzed health data from 23,000 Greek adults. They found that those who took a nap of at least 30 minutes three times a week were less likely to die of heart disease than those who never napped.

And now, the flip side of the coin. Studies have associated daytime napping with an increase in biomarkers of inflammation, impaired blood sugar control, unhealthy blood pressure, sleep disruption and an increased risk of cardiovascular disease. These adverse outcomes are sometimes linked to long daily naps. Others suggest a habit of long naps may be an early marker of cognitive decline. All of the research makes clear that age, health, fitness, genetics and lifestyle also play a significant role.

It is also important to note these are observational studies. These studies extrapolate conclusions from existing health data and not from direct experimentation. An observational study can suggest a correlation between certain factors, but it can’t prove or explain it. When it comes to the effects of napping on cardiovascular health, both sides of that equation are incredibly complex.

Sleep is made up of multiple stages, each with a distinct physiological effect on the body. The development and manifestation of cardiovascular disease is influenced by genetics, diet, environment and lifestyle choices. All of this makes it impossible to make a definitive statement regarding napping and cardiovascular health.

When it comes to napping for improved health, the consensus appears to be that brief naps a few times a week can have a beneficial effect. However, longer naps, particularly for people who are already struggling with overnight sleep, may be associated with cardiovascular risks.

(Send your questions to askthedoctors@mednet.ucla.edu, or write: Ask the Doctors, c/o UCLA Health Sciences Media Relations, 10960 Wilshire Blvd., Suite 1955, Los Angeles, CA, 90024. Owing to the volume of mail, personal replies cannot be provided.)

Kansas City, MO 64106; 816-581-7500