Ask the Doctors by Eve Glazier, M.D. and Elizabeth Ko, M.D

Circadian Misalignment Has Many Negative Health Effects

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, 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.)