Does Olive Oil Reduce Your Risk of Dying From Dementia?
Reading Time: 4 minutesIs Olive Oil Uniquely Good for Your Health? Maybe Not., A recent study seems to say yes. I’m very skeptical., Olive oil healthy: New research suggests that it lowers death risk. Be skeptical.
Every month or two, we are treated to a slew of news stories that tell us that a specific food is either great or terrible for our health. Red meat is bad; chile peppers are good. Broccoli is both saving and destroying lives. If you want to live longer, make sure you eat blueberries—but, wait, not those blueberries.
The most recent of these stories is one about olive oil, and it has popped up everywhere. Apparently, olive oil is the key to stopping people from dying of dementia as they age. An extra half a tablespoon of the fancy fat a day could knock a whopping 28 percent off your risk of dementia mortality!
Unfortunately for salad lovers (and bread dippers) everywhere, the truth isn’t quite as simple as that. It’s possible that olive oil is good for you, but it’s quite likely that this is yet another interesting association that doesn’t mean all that much to your life.
The research that has everyone excited about olive oil is a new nutritional epidemiology paper that looked at two large cohorts of people recruited and followed up on in the United States: the Nurses’ Health Study and the Health Professionals Follow-Up Study. The authors of the paper, which appeared in Nutrition, Obesity, and Exercise, looked at what these people reported eating, then compared the risk of dying from dementia over the course of 28 years for people who reported eating a lot of olive oil (11 grams, or about a tablespoon a day) with those who said they ate less of the stuff.
At the end of the study, the researchers found that people who reported eating a lot of olive oil were less likely to die from dementia. The ‘results suggest that olive oil intake represents a potential strategy to reduce dementia mortality risk,’ they write.
As nutritional epidemiology studies go, this one wasn’t bad. The authors controlled for a range of factors in their analysis, such as whether participants reported smoking or having other health conditions; they even controlled for other elements of their self-reported dietary intake. The researchers also ran a range of sensitivity analyses to try to rule out other factors that could be causing the findings.
And yet I’m still not recommending you go out and buy a gallon of olive oil. This sort of study is, by definition, complex. At the end of the day, it’s very hard to know if olive oil causes a lower risk of dementia death or if it’s just an association, despite the hard work of the authors.
Even taking the results at face value, olive oil isn’t a unique substance. The paper includes an analysis of the impact of replacing other fats with olive oil—if people in this cohort subbed mayonnaise out in favor of using olive oil, it helped. But the study found that canola and sunflower oils had the same protective effect as olive oil.
Further, and kind of weirdly, the authors show that olive oil didn’t just reduce the risk of dementia death. It also reduced the risk of dying, generally. Why not tout those findings? It’s relatively easy to understand how olive oil could plausibly help with dementia death risk, because of compounds that might reduce inflammation in the brain. (I’m still skeptical, but it’s at least possible!) It’s much harder to know how it could in any way relate to breast cancer or suicide risk. That it seems to is reason to take the findings with a grain of salt. The simplest explanation is that there is just something else going on with people who opt for olive oil, not that olive oil is a health elixir.
And the fact is, there’s only so much you can control for in this sort of study. For example, the authors didn’t actually have data on how wealthy the people in their study were. That data wasn’t gathered in the ’70s and ’80s, when these two cohorts were set up. In order to control for socioeconomics, the authors instead used an area-level measure, which calculates an average score for the neighborhood where the people lived, a stat that can be quite misleading when it comes to individuals. Someone’s neighborhood can offer you a guess at the size of their bank account, but not much more than that.
In addition, people are really bad at knowing how much they eat of specific things. The diet questionnaires that this kind of research relies on are notoriously problematic—they ask participants to recall what they’ve eaten from all kinds of food groups over the past several months. This means that the measure of olive oil intake that the authors cited may not accurately reflect how much of the stuff the individuals in the study actually ingested. Unless you’re cooking all your food and carefully measuring and recording each time you add olive oil, it would be very hard to provide a researcher with an accurate picture.
You also have to take into account the magnitude of the purported effect here. On average, over the decades of follow-up in these cohorts, about 24 out of every 10,000 people in the group who ate no olive oil at all died each year from dementia. For the people who ate lots of olive oil, that was reduced to 16 deaths per 10,000, or by less than a tenth of a percentage point. That’s not a large reduction in risk.
Finally, and perhaps most interestingly, the benefits of olive oil were seen only for women. In the Nurses’ Health Study, which was all female due to the decade in which it started, there was a 33 percent relative benefit for olive oil intake (though that relative benefit still tranMediaDownloaders to a very small reduction in deaths over thousands of women). In the Health Professionals Follow-Up Study, which recruited men, there was no detectable benefit for people who ate more olive oil.
It’s certainly possible that olive oil is good for your health. Of course, if the results of this study are to be believed, that’s true solely for women, and you could use other vegetable oils instead anyway.
What’s much more likely is that olive oil is simply associated with generally better health. You can control in these studies for the things you know about and measure, but not for the things you don’t or can’t. These studies are done not by keeping people in a lab for 28 years—humans are complicated, and it is basically impossible to ask them about every aspect of their lives and have them write that down accurately.
If you like olive oil, there’s no reason to stop eating it, but there’s also not much evidence that eating more of it will save your life.
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