It's fairly common for a medical treatment to cause side effects: think headache, upset stomach, sleepiness, and occasionally more severe side effects. Far more rarely, a side effect provides an unexpected benefit. This might be the case for the shingles vaccine.

Shingles is a painful, blistering skin rash caused by the varicella zoster virus responsible for chickenpox. The virus lies dormant in nerve tissue and can reactivate to cause shingles in anyone who has had chickenpox in the past. A vaccine to prevent shingles is recommended for adults ages 50 and older, and for people 19 and older who have an impaired immune system.

While we know the shingles vaccine is effective at preventing shingles, evidence is mounting that it might also reduce the risk of dementia. Yes, a vaccination to prevent shingles may lessen your risk of dementia.

Dementia is a devastating condition for those affected and their families. Currently, an estimated nine million people in the US have dementia. The number is expected to double by 2060, primarily because of the aging population. In most cases, no highly effective treatments are available. An effective preventive measure could have an enormous impact, especially if it's safe, inexpensive, and already available.

Some (though not all) studies have found that having shingles increases your risk of dementia in the future. And that's led researchers to explore the possibility that preventing shingles through vaccination might reduce dementia risk.

Several studies suggest this is true. For example:

Perhaps the best evidence suggesting that shingles vaccination prevents dementia comes from a natural experiment recently published in the journal Nature.

A natural experiment takes advantage of real-world circumstances by dividing people into an exposed group and an unexposed group and then comparing specific outcomes.

Natural experiment studies bypass the challenges of having to recruit hundreds or thousands of study subjects who might differ from one another in important ways, or who might alter their behavior because they know they're in a study. The results can be even more valuable than — and as credible as — standard randomized trials.

In 2013, Wales made the shingles vaccination available to individuals based on their date of birth: anyone born after September 2, 1933, was eligible, while anyone born before that date was not. Researchers took this opportunity to analyze health records of nearly 300,000 people: half were two weeks older than the cutoff date and half were two weeks younger. The study looked at whether people developed dementia over a seven-year period.

Researchers found that compared to those who didn't get the shingles vaccination, those who received it

A study of this type cannot prove that shingles vaccination prevents dementia. But along with the studies cited above, there's a strong suggestion that it does. We'll need additional studies to confirm the benefit. We also want to understand other details of the vaccine's effect, such as whether protection applies more to some types of dementia (such as Alzheimer's disease) than others, and whether the effect of vaccination changes over time.

With any unexpected finding in science, it's a good idea to ask whether there is a reasonable explanation behind it. Scientists call this biologic plausibility. In general, the more plausible a result is, the more likely it is to hold up in later research.

In this case, several lines of reasoning explain how a shingles vaccine might reduce the risk of dementia, including:

The observation that women had more protection from dementia than men after shingles vaccination is unexplained. It's possible that the immune response to vaccination is different in women, or that dementia develops differently in women compared with men.

All of us can take steps to lower dementia risk, mostly through healthy behaviors such as being active regularly and choosing a healthy diet. Evidence is mounting that shingles vaccination should be added to the list. It's a story worth following. Future studies of the shingles vaccine could even provide insights into how dementia develops, and how to better prevent and treat it.

Until then, get your shingles vaccination if you're eligible for it. It can prevent painful episodes of shingles — and may do much more.

Harvard Health Publishing

Not such good news for butter lovers like myself: seesawing research on how healthy or unhealthy butter might be received a firm push from a recent Harvard study published in JAMA Internal Medicine. Drawing on decades of data gathered through long-term observational studies, the researchers investigated whether butter and plant oils affect mortality.

One basic takeaway? "A higher intake of butter increases mortality risk, while a higher intake of plant-based oil will lower it," says Yu Zhang, lead author of the study. And importantly, choosing to substitute certain plant oils for butter might help people live longer.

The researchers divided participants into four groups based on how much butter and plant oils they reported using on dietary questionnaires. They compared deaths among those consuming the highest amounts of butter or plant oils with those consuming the least, over a period of up to 33 years.

Plant oils won out handily. A 15% higher risk of death was seen among those who ate the most butter compared with those who ate the least. A 16% lower risk of death was seen among those who consumed the highest amount of plant oils compared with those who consumed the least.

Higher butter intake also raised risk for cancer deaths. And higher plant oil intake cut the risk for dying from cancer or cardiovascular disease like stroke or heart attack.

While the study looked at five plant oils, only soybean, canola, and olive oil were linked with survival benefits. Swapping out a small amount of butter in the daily diet — about 10 grams, which is slightly less than a tablespoon — for an equivalent amount of those plant-based oils was linked with fewer total deaths and fewer cancer deaths, according to a modeling analysis.

"Butter has almost no essential fatty acids and a modest amount of trans fat — the worst type of fat for cardiovascular disease," Dr. Walter C. Willett, professor of epidemiology and nutrition at the Harvard T.H. Chan School of Public Health and professor of medicine at Harvard Medical School, noted by email.

By contrast, the plant oils highlighted in this study are rich in antioxidants, essential fatty acids, and unsaturated fats, which research has linked to healthier levels of cholesterol and triglycerides and lower insulin resistance.

Especially when substituted for a saturated fat like butter, plant oils also may help lower chronic inflammation within the body. Making such substitutions aligns with American Heart Association recommendations and current Dietary Guidelines for Americans for healthful eating that lower risk for chronic disease.

And for the butter lovers? "A little butter occasionally for its flavor would not be a problem," says Dr. Willett. "But for better health, use liquid plant oils whenever possible instead of butter for cooking and at the table." Try sampling a variety of plant oils, like different olive oils, mustard oil, and sesame oil, to learn which ones you enjoy for different purposes, he suggests. Additionally, a blend or mix of butter with oils — or sometimes a bit of butter on its own — can satisfy taste buds.

The study crunched data collected through a questionnaire answered every four years by more than 221,000 adults participating in the Nurses' Health Study, Nurses' Health Study II, and Health Professionals Follow-Up Study. As is true of all observational studies, this type of research can't prove cause and effect, although it adds to the body of evidence. Because most participants were white health care professionals, the findings may not apply to a wider population.

The researchers adjusted for many variables that can affect health, including age, physical activity, smoking status, and family history of illnesses like cancer and diabetes. The size of the study, the length of follow-up, and multiple adjustments like these are all strengths.

Harvard Health Publishing