When it comes to keeping the doctor away, apples could have some serious competition.

Based on new research, the adage could easily be changed to be “Two Brazil nuts a day keeps the doctor away.” That’s because according to the study, published in the American Journal of Clinical Nutrition, a deficiency in the mineral selenium is linked to a marked increase in liver cancer risk. And, you guessed it: Brazil nuts are an amazing source of selenium.

The researchers recognized that selenium deficiency is a widespread health concern that appears to be a risk factor for liver cancer and possibly other forms of cancer, although this study only examined the mineral deficiency’s effect on liver health. The researchers found that suboptimal selenium status may be linked to an appreciably increased risk of liver cancer—up to 10 TIMES the risk.

Eating a diet that contains adequate amounts of the mineral is not only critical to liver health and cancer prevention, it is also imperative to fertility and reproduction, thyroid hormone synthesis, immunity and DNA health. The mineral is also a potent antioxidant that helps to scavenge free radicals before they can damage the body’s cells and tissues.

Earlier studies in the journal Biomedical and Environmental Sciences show that adequate selenium intake also reduces skin cancer risk.

Some of the symptoms of selenium deficiency include: immune weakness, gastrointestinal (GI) problems, hair loss, diarrhea, cirrhosis, fatigue and mood swings. As with many nutritional deficiencies and medical conditions, there can be overlap in symptoms so having these symptoms does not necessarily mean you have a selenium deficiency. Conversely, if you have these symptoms you should consult your physician to rule out any other possible health conditions.

Selenium-Containing Foods

Oysters, tuna, whole grains, sunflower seeds, crimini mushrooms, poultry and eggs are all good sources of selenium; however Brazil nuts are by far the best. Just one ounce of these nuts (about 6-8) contains 544 micrograms of selenium. The recommended daily intake is 55 micrograms for adult males and females; however, pregnant and lactating women require 60 to 70 micrograms, respectively.

Selenium is also available in supplement form: as either selenomethionine or selenite. Selenomethionine is the more absorbable form of this mineral. Keep in mind that selenium can build up in tissues and can become harmful in excessive doses.

While an apple a day is still a good idea, you might want to add some Brazil nut butter or a handful of raw, unsalted Brazil nuts to round out the healing properties of this classic snack.