Dear Doctor: I’ve been eating a vegan diet for about a year. My mom says she read that vegans don’t get enough choline, and that’s dangerous. Is this true? What is choline, and where does it come from?

Dear Reader: Choline is an essential nutrient that is abundantly available in animal-based products such as eggs, dairy products, beef, chicken and fish, and in somewhat smaller concentrations in vegetables, legumes and grains. It’s the source of chemical compounds known as methyl groups, which circulate in the body and play a role in the proper functioning of numerous metabolic processes in the brain and nervous system, including mood, memory and muscle control.

Choline is vital to the proper structure and performance of cell membranes, including those in the brain, and it is important in gene expression. It has been linked to lower levels of chronic inflammation, and offers protective properties in certain types of heart disease. It’s also important in early development.

Although choline is produced by the liver, the quantities are not adequate for the body’s daily needs. That’s what makes it an “essential nutrient.” There is no recommended daily allowance for choline. Instead, a guideline known as Adequate Intake, or AI, has been established. For adults, the AI is 425 milligrams per day for women and 550 milligrams per day for men. For children, the number ranges from 125 milligrams per day for infants to 375 milligrams per day for young teens. Because choline is so important to development, women who are pregnant or nursing need more of the nutrient.

According to the National Institutes of Health, most people in the United States, whether vegans, vegetarians or omnivores, fall short on consumption of the nutrient. And while it’s true that animal-based foods have the highest levels of choline, plant-based sources are also widely available. Certain vegetables, beans and grains are good sources of choline. For example, one-half cup of roasted soybeans has almost as much choline as 3 ounces of lean beef. One-half cup of broccoli has only slightly less choline than 1 cup of low-fat milk. A cup of cauliflower has as much choline as 3 ounces of grilled chicken.

If your personal preferences steer you away from choline-rich foods, you can consider making up the shortfall with supplements. Just be sure to stick to the dietary guidelines and not to go overboard. Too much choline can result in nausea and vomiting, excess sweating and salivation, low blood pressure and liver problems.

The bottom line here, as always when we’re talking about health and nutrition, is to avoid the empty calories in the snack food aisle and the fast food drive-through, and focus instead on eating and cooking from a wide range of whole foods. Your body -- and, we suspect, your mother -- will thank you.

(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: One of the moms in our car pool had to drop out because she has a frozen shoulder. I’ve never heard of that. What is it, and how did she get it?

Dear Reader: Frozen shoulder, also known as adhesive capsulitis, is a common and painful condition in which the connective tissues around the shoulder joint gradually become thickened and inflamed. It’s more common in women than men, and it more commonly occurs in people from ages 40 to 60. With a frozen shoulder, previously simple activities like raising your arms to slip into a T-shirt or even reaching up to scratch your head become very difficult.

To understand the condition, let’s start with the shoulder joint itself. It’s a ball-and-socket joint, which means that the rounded head of the humerus, which is the upper arm bone, fits into a cuplike structure located on the scapula, or shoulder blade. Cartilage, which is smooth and elastic, covers the surfaces of the bones where they meet. It acts as a shock absorber, and its sleek surface helps to reduce friction and smooth movement. Meanwhile, strong ligaments that attach to the “ball” of the humerus and to the shallow “socket” on the scapula hold the parts of the shoulder joint in place. Taken together, this allows for a wide range of motion. In fact, the ball-and-socket joint offers the most freedom of movement of any type of joint in the body.

When inflammation causes the connective tissues within the shoulder joint to become thick and stiff, the capsule tightens. In some cases, scar tissue forms, which further limits range of motion. All of this makes any kind of movement within the joint, whether active or passive, both difficult and painful.

Frozen shoulder can develop when injury, trauma or surgery have forced long-term immobility. It is also seen more often in people at risk of developing diabetes, and those with chronic inflammatory arthritis. The condition begins with localized discomfort or pain, which gradually increases over time. It can take from two to 10 months for a frozen shoulder to develop. During the “frozen” stage of the condition, which can also last for months, the joint becomes difficult, if not impossible, to move. The good news is that during this time, pain from the condition may decrease. Eventually, range of motion begins to return to the joint.

In order to eliminate other potential causes, imaging tests like an MRI or an X-ray may also be used. Treatment focuses on alleviating pain and recovering range of motion. This entails the use of various anti-inflammatory medications, and possibly injections of corticosteroids into the joint capsule. Patients are also taught exercises to stretch the joint capsule, and when recovery begins, strengthening exercises. Infrequently, surgery may be required. Most cases of frozen shoulder resolve within a year or two.

(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: Is wildfire smoke really that dangerous? We’re in northern Idaho and our town has been handing out face masks, but I’ve heard they don’t really do much. What should I do to keep our family safe?

Dear Reader: The smoke from wildfires does indeed pose a significant health threat. This is true whether you live near an active fire zone, or are in a town or city hundreds of miles away. Wildfire smoke rises to high altitudes and can thus be carried great distances.

When wildfire smoke drifts to earth in urban areas, it mixes with existing pollutants and elevates ozone levels. The smoke itself contains billions of minute particulates, which can adversely affect heart and lung health. There is now enough data to make the connection between wildfire smoke and a worsening of respiratory conditions like asthma, chronic obstructive pulmonary disease and allergies, and an increase in heart attack risk. The very young, the elderly and the medically frail are at especially high risk.

Breathing the minute particles found in wildfire smoke can result in wheezing, coughing, congestion, sneezing, throat and lung irritation, runny nose, watery eyes, shortness of breath and chest discomfort. The particulates in wildfire smoke are so small, they can reach deep into the delicate tissues of the lungs and set off an inflammation reaction. Since the airways of people living with asthma, COPD and allergies are chronically inflamed, even low levels of ambient wildfire smoke can make their conditions worse.

To protect against wildfire smoke, stay indoors as much as possible. Make sure all windows, doors, skylights and fireplace flues are kept tightly closed. Air conditioners or HEPA filters will help. While you’re inside, minimize indoor pollution. That means no vacuuming or use of aerosol sprays, scents or candles.

Anyone who relies on a rescue inhaler should make sure to have one ready, plus a spare in case it’s needed. Whether you’re indoors or out, avoid unnecessary exertion. If you do go outside for any length of time, it’s recommended that you change into clean clothes when you return indoors to prevent particulates from getting into the indoor air.

It’s natural to turn to a face mask for protection. However, the type of mask that you use makes all the difference. Dust masks and bandanas are porous and will catch only the largest particles, like ash and debris. The only masks that are capable of blocking the fine particulates associated with wildfire smoke are masks that are rated N95 or N100. It’s important that these types of masks make a full and complete seal around the perimeter. Any gaps will allow particulates to enter and defeat the purpose. Also, please note that breathing with these types of masks can be strenuous. It’s recommended that you choose one outfitted with an exhalation valve, which also reduces heat buildup.

Be sure to monitor your local air quality. If the symptoms described above persist, seek medical care 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.)