A snacking staple could be behind the rise of cancer in the US – unknowingly fueling the surge of the disease among young people.

Brazil nuts, common nuts chock full of antioxidants, contain beneficial minerals and nutrients. They are a good source of B vitamins, calcium, zinc, magnesium and vitamin E. 

The nuts are high in fiber and low in monosaturated fats, helping to lower cholesterol and improve heart health, as well as reduce stroke risk. They are also said to ease inflammation in the body, strengthen bones and improve cognition.

One essential mineral in Brazil nuts, selenium, is believed to boost the immune system and support thyroid function, but too much of it could actually have the opposite effect and be harmful to your health. 

People 14 and older are advised to get 55 micrograms (mcg) of selenium per day. The recommendations for babies, children and young teens range from 15 mcg and 40 mcg per day. 

Selenium does have benefits, but it is easy to over consume this powerful mineral, and Brazil nuts contain a very high concentration of it – about 544mcg per 1oz portion, which is typically just six nuts.

Due to this high content, people are cautioned to not consume more than one to two nuts per day, as too much selenium has been linked to difficulty breathing, tremors, kidney failure and heart attacks. 

And while previous research has suggested selenium has cancer preventative properties, newer studies actually suggest the opposite – it may increase the risk of developing the disease.  

Brazil nuts contain a very high concentration of selenium – about 544micrograms per 1oz portion, which is typically just six nuts.

The daily recommended value of the mineral is also readily available in tuna, sardines, shrimp, beef, pork, turkey, eggs and spaghetti – but these can be enjoyed without worrying of overdosing on selenium.  

Dr Steven Quay, a physician-scientist specializing in cancer research, called selenium a ‘double-edged sword.’

He told DailyMail.com: ‘On one hand, it’s a vital trace mineral your body uses for DNA synthesis, thyroid function, and immunity. On the other? Cross the 400 mcg/day line and you’re flirting with selenosis — garlic breath, brittle nails, and worse. 

‘Some studies praise it for neutralizing mercury’s toxicity, while others warn: “Not a cancer shield, folks.” The truth? Dose matters. Like all powerful tools, it’s about balance — not abundance.’

While people only need a small amount of selenium, it does play an important role in the body. It is involved in the production and protection of DNA, and, according to the NIH has been shown to boost cognitive scores in older adults and improve sperm motility.

Dr Martina Ambardjieva, a urologist, told DailyMail.com: ‘Selenium does have benefits when taken in limited, doctor-recommended amounts.’

However, consuming too much – the NIH says the upper safe limit for people over 14 years old is 400 mcg – can lead to selenium toxicity and cause a wide array of symptoms. 

These, Dr Ambardjieva said, include nausea, vomiting, diarrhea, hair loss, diseased nails, rotting teeth, arthritis and inflammation. 

It is not known how many cases of selenium toxicity are recorded each year.  

Despite the dangers, because of selenium’s DNA protective properties, the mineral has long been thought to play a role in the prevention of cancer. 

But a comprehensive review on the matter found different.  

A 2018 Cochrane review called Selenium for Preventing Cancer examined whether selenium intake or supplementation reduces cancer risk. 

Analyzing data from 10 studies involving over 27,000 people, the review found there was no evidence that selenium supplements decrease cancer incidence. 

Additionally, the researchers said some of the studies included in their review ‘raised concerns’ because they reported a higher occurrence of prostate cancer and type 2 diabetes in people taking a selenium supplement. 

Not only does the mineral not prevent cancer, but other studies show it could actually increase risk.

The daily recommended value of selenium is also readily available in supplements, as well as foods like tuna, sardines, shrimp, beef, pork, turkey, eggs and spaghetti

Above is a graph showing the increase in cancer rates among people younger than 50 (the blue line represents women and the green line represents men)

A 2024 study published in the journal Nature found people with both the lowest and highest intake of selenium had a greater chance of developing cancer. 

After analyzing nearly 3,000 people from a database in Vietnam, researchers found the ‘safe’ intake level of selenium was 111 mcg to 124 mcg per day.

People who consumed 28 mcg to 77 mcg and those who took in 169 mcg to 332 mcg both had an increased risk of developing cancer. The association was highest for stomach, colon, rectum and lung cancers. 

For high-intake, the odds of developing cancer were 86 percent higher. While chances were three times higher in the low-intake group. 

Research from 2002 found the group of people with the highest levels of selenium in their blood – 122 or higher ng/ml (nanograms per milliliter) – had a 20 percent elevated cancer incidence. People in the two low-dose groups – less than 122ng/ml – showed a 30 to 49 percent reduction in cancer incidence, however. 

And a third separate study found selenium supplementation was associated with ‘statistically significant’ elevated risk – a 25 percent increase – of squamous cell carcinoma – the second most common type of skin cancer. 

Additionally, health officials warn selenium can impair the effect of immunosuppressants, birth control and cholesterol medications, while exacerbating the effects of anticoagulants and sedatives. 

Due to the wide range of results and, at times, contradictory conclusions, experts say more research is needed to examine the relationship between selenium and cancer. 

Until then, it is recommended to only take the doctor-advised dosing.