Likewise, increased use of the osteoporosis drug raloxifene (Evista), which has also been shown to have a protective effect against breast cancer, could have played a role.

CNN: Falling breast cancer rates: What's behind the numbers?

At that moderate level, alcohol can have a protective effect on your heart.

CNN: updated

There is little evidence to show that handguns have a protective effect.

FORBES: Connect

"Importantly, even partial adherence to statin therapy conveys a mortality benefit, suggesting that statins do not need to be taken daily to have some protective effect, " said Dr Francis.

BBC: 'Give out statins with junk food'

Researchers at Rush Medical University found that mentally challenging activities, such as reading and playing chess, may have a protective effect on the brain and help lower risk of dementia associated with Alzheimer's disease.

CNN: Vital Signs health tips

Researchers don't know why a plant-based diet seems to have a protective effect, but one likely reason is the nutrient profile of vegetarian diets, which tend to be higher in fiber and lower in saturated fat.

WSJ: Vegetarians Live Longer Than Meat-Eaters, Study Finds

Some, but not all, previous studies have shown a protective effect of pre-eclampsia on breast cancer, although such research has been carried out mainly in northern Europe and North American populations.

BBC: NEWS | Health | Pregnancy disorder link to cancer

But while there is pretty much consensus within the scientific community about the protective effect these oils have on the heart, their impact upon the brain - whether to lift depression, curb violent urges, or simply to boost concentration - are less well documented.

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