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Mayo Clinic Q&A: vitamin D; secondhand smoke

VITAMIN D GUIDANCE VARIES

I have heard different recommendations from different sources regarding vitamin D. One doctor told my husband that everyone living in the Northern Hemisphere should take a vitamin D supplement every day, even in the summer. What do you recommend?

Understanding how much vitamin D you need can be confusing because there are different recommendations about how much vitamin D adults should get. Using the recommendations that fall on the low end, many adults don't get the amount of vitamin D they should. Because few foods contain vitamin D naturally, eating foods fortified with vitamin D and taking a supplement may be beneficial.

Vitamin D is important because it helps your body sustain normal levels of calcium and phosphorus. Because it works as a key that allows your body to absorb calcium, vitamin D plays a critical role in forming and maintaining healthy bones. It also helps keep your muscles, nerves and immune system healthy.

Research suggests that consistently getting enough vitamin D can significantly lower the risk for the bone-thinning disease osteoporosis. Low vitamin D also is associated with falls, multiple sclerosis, rheumatoid arthritis, chronic pain, diabetes, high blood pressure, cardiovascular disease and some cancers. However, an association does not mean low vitamin D causes these conditions, or that taking a vitamin D supplement will adequately prevent or treat them.

Vitamin D is found in some foods, such as egg yolks, cheese, cod liver oil, beef liver and fatty fish like tuna, salmon, sardines, herring and mackerel. But the amount of vitamin D in these foods is quite small. In the United States, many people get the bulk of their dietary vitamin D from foods that are fortified with it, including milk, cereals and some brands of yogurt and orange juice.

In general, even with fortified foods, diet usually doesn't provide enough vitamin D. And certain health conditions that affect the gastrointestinal tract may decrease the absorption of vitamin D and predispose one to low vitamin D blood levels. You also can get vitamin D through direct exposure to sunlight, although the amount of sun you need to get enough vitamin D can vary greatly.

For people in northern climates or those who spend most of their time indoors, adequate exposure to sunlight can be hard to get. Also, if you regularly wear sunscreen with a sun protection factor higher than eight — a wise move to protect your skin from cancer — or if you have a darker skin tone, you may not be absorbing vitamin D, even when you are out in the sunshine.

Recommendations for how much daily vitamin D adults need through diet have changed over the years. Currently, different recommendations exist. The Institute of Medicine has placed the recommended dietary allowance, or RDA, for vitamin D at 600 international units (IU) per day for young adults and 800 IU per day for adults older than 70. Other experts suggest that adults' vitamin D needs are much higher. For example, the Endocrine Society recommends up to 1,500 to 2,000 IU of vitamin D daily for adults.

Mayo Clinic recommends that adults get at least the RDA of 600 IU. However, 1,000 to 2,000 IU per day of vitamin D from a supplement is generally safe, should help people achieve an adequate blood level of vitamin D, and may have additional health benefits. While there are no guidelines for checking your vitamin D blood level, it may be prudent in people with osteoporosis or certain other health conditions. Discuss with your health care provider if it may be beneficial to check your vitamin D level.

If you have ongoing health concerns or a chronic health condition, talk to your health care provider before you begin taking any dietary supplement, including vitamin D. He or she can help you decide if supplements are appropriate for your situation.

Donald Hensrud, M.D., M.P.H., Preventive Medicine, Mayo Clinic, Rochester, Minn.

STAY AWAY FROM SECONDHAND SMOKE

Is secondhand cigarette smoke dangerous to my health?

The short answer to your question is yes, secondhand smoke is dangerous. Secondhand smoke, also known as environmental tobacco smoke, is a combination of the smoke coming from a burning cigarette and the smoke exhaled by the smoker, which spreads out to the surrounding space.

Secondhand smoke contains the same toxic chemicals that are inhaled by smokers, including nicotine, carbon monoxide, benzene, formaldehyde, cyanide and a variety of cancer-causing substances. The effects of these chemicals are greater when inhaled directly from a cigarette; nonetheless, the effects are still toxic secondhand.

Particles in secondhand smoke can remain in the air for hours, and the residue that clings to a smoker's hair, clothing and other items also may pose health risks, especially for children. This residue is sometimes referred to as thirdhand smoke.

Because secondhand smoke is a dynamic mixture that changes as it travels and mixes with the environment, it's hard to quantify its risk. In general, no amount of secondhand smoke is safe, because of its inherent toxicity.

Evidence indicates that the secondhand smoke exposure that comes from living with a smoker can increase your risk of lung cancer by 20 to 30 percent. Secondhand smoke also increases your risk of coronary heart disease by 25 to 30 percent and can lead to a variety of health risks for children, as well as for pregnant women and their unborn babies.

As with active smoking, the greater the exposure — and the longer the duration of exposure — the greater the risk of harm, especially for diseases such as lung cancer. However, even short-term exposure can worsen symptoms of asthma and coronary heart disease.

Unfortunately, air-cleaning devices or filters don't effectively clear the air of secondhand smoke. The only way to eliminate the risks of exposure is to eliminate smoking. In recent years, smoke-free legislation has greatly increased the number of public places that are now smoke-free.

For a smoker, smoking cessation can be a difficult journey but an important one. If you smoke, know that quitting will improve not only your own health, but also the health of your loved ones. If you live with a smoker, your full support is essential to his or her quitting process.

Steven Ames, Ph.D., Psychology, Mayo Clinic, Jacksonville

(Adapted from Mayo Clinic Health Letter)

Mayo Clinic Q & A is an educational resource and doesn't replace regular medical care. Email a question to MayoClinicQ&[email protected] For more information, visit mayoclinic.org. © 2017 Mayo Foundation for Medical Education and Research. Distributed by Tribune Content Agency LLC. All rights reserved.

Mayo Clinic Q&A: vitamin D; secondhand smoke 04/27/17 [Last modified: Monday, May 1, 2017 5:25pm]
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