Thursday, April 12, 2012

Olive Leaf and Hypertension

Recently, I found myself leafing through a freebie natural health magazine – if you read this blog, you probably know the type – and came across an article about the use of olive leaf in hypertension. The article was a bit alarmist, and suggested that medical doctors were playing a dangerous game by allowing elevated blood pressure to go untreated. On the contrary, anyone familiar with the creation of ‘prehypertension’ as a diagnostic category or with updates in cholesterol treatment guidelines, knows that when it comes to cardiac risk factors, MDs are nothing if not aggressive. So I walked into the article with a bit of skepticism. However, given that I’d just blogged last week about using magnesium in hypertension, I thought I’d do some investigation into olive leaf and hypertension.

Olive leaf is a little-known herb, but one which has interested me since I read an article stating that it had been shown to inhibit viral reverse transcriptase – one of the enzymes that is crucial to HIV’s ability to infect humans. It’s been variously lauded as an antioxidant, an antimicrobial, and anti-inflammatory. I, however, am primarily interested in its activity as an antihypertensive.

As always, research starts with animal studies. About a decade ago, researchers found that olive leaf extract could reverse hypertension in lab rats who had been made hypertensive through administration of a nitric oxide-synthase inhibitor. While this information is interesting, there exist too many variables to consider this for application to humans – human hypertension arises from a variety of causes and mechanisms, and nitric oxide inhibition is not a common cause – had the rats been hypertensive due to obesity or dietary factors, I would have given the study more consideration, but given the experimental design, it could have easily been inferred that the olive leaf extract merely inhibited the inhibitor, and wouldn’t be useful in humans.

As if noting the limitations of the prior research, a subsequent article addressed this exact question, and found that an extract of olive leaf was effective in preventing severe hypertension in salt-sensitive, insulin-resistant lab rats. This is much more compelling information – these rats have metabolic problems which more closely resemble the ones plaguing Americans, and their hypertension arises from similar causes. This study had me more interested. That said, a more recently published article found that olive leaf extract, when included in the diet of rats fed a high-carbohydrate, high-fat diet, improved a number of markers of cardiac and metabolic markers, including blood lipids, glucose tolerance, and organ changes, but without affecting blood pressure. This study used a model that even more closely mimicked human hypertension, and found no effect on blood pressure. Taken together, these animal studies are interesting, but equivocal.

Eventually, human studies were performed. A 2008 study found that an olive leaf extract did reduce blood pressure in humans, with the greatest changes being a 9 mmHg drop in systolic hypertension, and 4 mmHg drop in diastolic. The study was small, and included only 40 participants, who were assigned to one of three study arms, so this isn’t earth-shattering evidence. Additionally, the evidence only shows a modest reduction in blood pressure, an amount that could be also achieved by diet and lifestyle changes, and the data comes from patients with borderline hypertension, not more severe disease, so it’s hard to tell how useful olive leaf would be in patients with a greater need for aggressive treatment.

The only other human study I was able to find was a 2012 study, which showed that olive leaf extract produced blood pressure decreases of 11.5 mmHg systolic and 4.8 mmHg diastolic in patients with Stage I hypertension. Again, this information does make me pay attention, as it satisfies some of the qualms I had with the earlier study, and the changes in blood pressure are closer to clinically important changes. Even so, there are significant problems with this study, including its being sponsored by makers of the olive leaf extract and a lack of ‘p-values’ or confidence intervals (tools used by researchers as measures of a study’s validity). An interesting study, to be sure, but not the piece of rock-solid evidence that would nail it for olive leaf and hypertension.

The obvious conclusion to all of this is that olive leaf is not yet ready for prime time when it comes to hypertension. The animal studies are intriguing, but the human studies are too small and too unreliable to make clinical judgments on them. Additionally, there is such great number of scientifically-validated ways of reducing blood pressure naturally, that it’s not necessary to turn to something with a less-established track record.

The additional moral to this story is that you can’t always trust what you read in ‘grey’ literature, especially when they are trying to sell you something. Results are overstated and limitations often go unmentioned in these reviews, and without direct access to the studies they are citing, it can be hard to sort out truths. Olive leaf may yet hold promise for the future, but dealing with a chronic condition is never as simple as taking a supplement a couple of times and being done with it – these conditions often require years of work to manage, and the therapeutic benefit of working with a qualified practitioner is crucial to successful outcomes.