Hello dear readers, and welcome to our first letters column of spring. We hope you’re enjoying the lengthening days and are recovering from the jolt of losing an hour to Daylight Saving Time. Speaking of which, we received mail regarding a recent column about the negative health effects of night shift work. These include fatigue, depression, cognitive lapses and an increased risk of heart disease, diabetes and certain cancers. This arises from the disruption of the circadian rhythm, or internal clock, which regulates our biological processes. Our internal clock oversees physiological functions at the molecular level, including cell regeneration, immune response and hormone production, and research shows no amount of extra sleep can "fix" circadian misalignment.

-- A reader from Port Neches, Texas, asked about rotational shift work, which is when day shifts and night shifts are interspersed. Although he had been comfortable working a sustained night shift schedule, he was recently assigned alternating sets of day and night shifts. “Shifting back and forth between days and nights leaves me fatigued,” he writes.

The answer is that rotational shift work, whether on a daily, weekly or even monthly schedule, makes the adverse physical effects of night shift work even worse. The circadian cycle is a powerful force, and our bodies never truly make peace with living outside of its natural rhythms. Any adjustments we are able to make take place only gradually, and over time. This means with each switch to a new schedule, our bodies start from scratch to make the slow adjustment. When work schedules change too often, our bodies just can’t catch up.

-- A reader who has been treated twice for basal cell carcinoma on her nose now uses an SPF 50 sunscreen with a high zinc oxide percentage. “I apply it every day, regardless of the weather -- whether clear and sunny or cloudy and overcast,” she writes. “But my weather app frequently shows a UV index of zero or 1. Does this mean I do not need to wear sunscreen?”

Please, do keep slathering on the sunscreen. A UV Index of zero to 2 means that for the average person, danger from the sun's UV rays is low. However, for those who burn easily or have had skin cancer, a full-spectrum sunscreen of at least SPF 30 is recommended.

-- In response to a column about healthy eating, a reader asked about fresh versus frozen produce. “I buy a lot of vegetables because I want to eat better,” she wrote. “But because I’m so busy, they sometimes go bad before I can cook them. Is frozen food so much worse for me?”

In good news for your wallet, a recent study by food scientists at the University of California, Davis found no significant nutritional differences between fresh and frozen fruit and vegetables. In fact, in some cases, as with vitamin E, frozen produce actually had higher levels of the vitamin than did fresh foods.

And all too quickly, we’ve run out of room. We love hearing from you, both the good (thank you!) and the critical.

(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 New York recently banned something called activated charcoal from all food and beverages. What is that, and why on Earth would anyone ever want to ingest it?

Dear Reader: The history of food fads is as long as it is strange. Back in the 11th century, after William the Conqueror successfully led the Norman conquest of England, he tried to conquer a weight problem with a liquid diet consisting mainly of alcohol. Lord Byron, the British poet and politician, was so enamored of vinegar as a curative that he made it the cornerstone of his diet and sparked a widespread fad. In the 1830s, Americans were urged to eat a bland diet anchored by graham crackers to cool their sex drives. And in the Victorian era, women downed pills that supposedly contained a tapeworm egg (they probably didn’t) so the parasite growing in their intestines would take care of any excess calories.

Now comes activated charcoal, the latest in a centurieslong preoccupation with magical thinking about food. The substance is made by heating carbon-rich materials like wood, peat or coconut shells to extremely high temperatures. The resulting charcoal is then ground up and stripped of extraneous molecules, which creates ultra-fine particles full of holes and crevices. These increase the surface area of each minute particle, which makes available thousands of potential binding sites. Thus "activated," the charcoal can now attract molecules, ions or atoms, making it a highly effective purifier. Activated charcoal is used in water filtration, and it is a go-to treatment in many cases of overdose and poisoning.

When added to food -- the coconut variety is most widely used in this instance -- activated charcoal transforms the familiar color palette of white, beige and brown to a startling dark black. From ice cream, smoothies and sauces to burger buns, beverages and pizza crust, an ever-growing range of everyday edibles is getting the activated charcoal treatment.

To be fair, much of the current rage for charcoal-infused foods arises from their visual shock value. But due to its ability to absorb impurities, activated charcoal has been assigned a wide range of health benefits, not all of them accurate. Some animal studies have suggested that activated charcoal may reduce certain damage associated with chronic kidney disease. There is evidence that it can ease intestinal gas, though the mechanism remains unclear. Claims that activated charcoal will clear the body of toxins or decrease bad breath remain unproven.

It can present some dangers as well. The same absorbent properties that make activated charcoal effective for poison control can also interfere with the absorption of medications. It can also cause constipation.

Still, it’s easy to understand how this latest food fad took hold. It’s also not surprising that it has become a target for regulation. Last spring, the Department of Health in New York City banned the use of activated charcoal in commercial food and drink. Health officials in San Francisco are also looking into addressing the trend. Advocates of activated charcoal have pledged to push back. It will be interesting to see what happens next.

(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: We’re used to hearing about the measles outbreaks that happen in areas where parents have refused to let their kids get childhood vaccinations. Is it true that now a kid wound up with tetanus for the same reason? That sounds so dangerous.

Dear Reader: You’re referring to the case of a 6-year-old boy in Oregon who developed tetanus after getting a gash on his forehead while playing on his family’s farm. The event actually took place in 2017, but a recent write-up of the case has pushed it into the headlines.

About a week after the parents cleaned and stitched up the boy’s cut, he developed troubling symptoms. In addition to involuntary muscle spasms, he couldn’t unclench his jaw and had difficulty breathing. Doctors at a regional medical center diagnosed him with tetanus, a disease for which he had not been vaccinated. His was the first case of tetanus in the state in more than 30 years.

Tetanus is a disease of the nervous system caused by one of two toxins that are released by a bacterium called Clostridium tetani. Spores of C. tetani are found in the feces of a number of animals, including cattle, horses, sheep, dogs, cats and chickens, and in contaminated dust and soil. The bacterium enters the body via a wound that has broken the skin, like a cut or a puncture, then releases a toxin called tetanospasmin, which impairs the motor neurons.

As the neurotoxin travels through the circulatory system, it binds to nerve endings in certain sites throughout the body. Once this occurs, there is no known way to clear the toxin from the nerve endings. The only treatment is to manage the painful and dangerous symptoms that the toxin causes while waiting weeks -- or even months -- for new nerve endings, which are toxin-free, to grow.

The effects of the tetanus neurotoxin are severe and life-threatening. The muscle spasms it causes can be sustained and powerful enough to cause a bone to break. Spasms of the muscles of the respiratory system and of the vocal cords interfere with breathing and often require an alternative airway and mechanical breathing support.

In the case of the Oregon boy, he experienced muscle spasms so severe they caused his spine to arch backward. His breathing was compromised, and he spent more than a month on a ventilator. Over the course of the eight weeks he spent in the hospital, he was tended by more than 100 nurses and doctors, none of whom had ever seen a case of tetanus before. Although having tetanus does not confer immunity, the boy’s parents reportedly refused to immunize him.

Tetanus is a preventable disease, and the Centers for Disease Control and Prevention recommend vaccines for people of all ages. Children receive tetanus protection via the DTaP vaccine, which covers diphtheria, tetanus and pertussis (whooping cough). It is recommended for babies at ages 2, 4 and 6 months, and again at 15 through 18 months old. The CDC also recommends a booster shot for children ages 4 through 6 years old. Adults need a tetanus booster every 10 years to stay protected.

(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.)