Tea and cardiovascular disease

The edition before the last of World Tea News talks about an article in the American Journal of Medicine that suggests that consumption of tea may help prevent both calcium deposition in coronary arteries and cardiovascular events.*

Interesting news, so I thought I should take a look at the original article, which was published on line September 15, 2016.** In this post, I will talk about the baseline data, with follow-up data discussed in future posts.

The article is based on data from the Multi-Ethnic Study of Atherosclerosis (MESA). This study was prospective, which means that it followed a sample of 6814 men and women aged 44 to 84, at 6 different U.S. medical centers. It  began in 2000, finished recruiting participants in 2002, and ended on December 31st, 2013. For the present analysis, data from 6508 people were used.

Participants provided dietary information when they entered the study and every 9 to 12 months thereafter. Computed tomography scans of the degree of coronary artery calcification were done at the beginning of the study and at 4 times thereafter. Not everyone participated at each scan, and it is not clear from the write-up whether everyone was actually scanned twice. That said, the analysis took into account the time between the first and the second scan in order to obtain information about changes over time. 

Another feature of the study was the attempt to take into account a multitude of factors that are known to contribute to cardiovascular disease (CVD), for example smoking, in order to tease out the contributions of tea, coffee, and total caffeine consumption to CVD.*** On the other hand no effort was made to distinguish among types of tea consumed or between caffeinated and decaf coffee.

So what do the baseline results tell us? 

First, it is striking, though not too surprising, that the people who had calcification in their arteries at baseline were older and more likely to be white and male than people who had none, and for the most part they were experiencing the known predictors of cardiovascular disease, such as hypertension, diabetes, and family history of coronary heart disease, “good” and “bad” cholesterol levels, and exercise time per week. Notable exceptions: there was no association with body mass index, though the mean was on the high side at 28.2±5.4; the people with no calcification actually ate slightly more fat, and other dietary measures, such as vegetable and fruit consumption, had a minor effect if any—hard to tell from the data given.

CT scan of the chest in cross section (the person's back is below the bottom of the picture), showing calcification in a coronary artery, from https://www.dic-kc.com/blog/2016/heart-health-ct-coronary-calcium-score. This link leads to another  from the Mayo Clinic that discusses how calcification is scored and what it means.

Now for the relationship with tea:

First, 58% of the participants did not drink tea at all, and another 29% drank less than a cup a day—only 13% drank tea on a daily basis…why this huge difference is not explained, of course, but the authors suggest that there may be other unmeasured differences, possibly lifestyle differences, that contribute to both the choice to drink tea and any results concerning arterial calcification and CVD. 

Next, to the calcification results: of the 800 people who drank tea daily at the time of enrollment into the study, about half had no measurable calcification in their arteries and half had some. For further analysis, the authors used a cut-off score which divided people into those who had relatively little to no calcification and those who had significant calcification.

While 13% of the participants drank tea each day, they accounted for slightly more of the participants (at 14%) who did not have significant calcification in their arteries according to their cut-off, and slightly fewer (at 11%) of those with significant calcification at baseline. The big finding is that when the authors took into account (= controlled for) all the cardiovascular risk factors, including age, drinkers of a daily tea had a lower risk of having the larger amount coronary artery calcification. 

Finally, people who drank tea daily at enrollment had fewer cardiovascular events during follow-up—12.3 events per thousand person-years for those who didn’t drink tea at all versus 7.7 events for those who drank tea every day. The difference is slight, but perhaps meaningful, but clearly drinking tea does not . Note that for this analysis, people of Chinese descent were excluded, because they consumed large amounts of tea…and also had fewer cardiovascular events! Which makes one wonder…was their advantage dietary or genetic or both?

When you think about these results, remember how few people drank tea on a daily basis in this study, and remember that those who drink tea may be doing a lot of other things differently or may be different genetically as well. 

So drink your tea for enjoyment—and just maybe you’ll get some cardiovascular benefits as well.

* http://worldteanews.com/tea-health-education/moderate-tea-consumption-shows-heart-benefits?NL=WTM-001&Issue=WTM-001_20161004_WTM-001_988&sfvc4enews=42&cl=article_4_b

** Miller PE, Zhao D, Frazier-Wood AC, Michos ED, Averill M, Sandfort V, Burke GL, Polak JF, Lima JAC, Post WS, Blumenthal RS, Guallar E, Martin SS, Associations between Coffee, Tea, and Caffeine Intake with Coronary Artery Calcification and Cardiovascular Events, The American Journal of Medicine (2016), doi: 10.1016/j.amjmed.2016.08.038. 

*** Here’s the complete list: age, sex, race/ethnicity, education, smoking (never, former, current), physical activity, total fat, alcohol consumption, fruits quartiles, vegetables quartiles, red meat quartiles, systolic and diastolic blood pressures, use of antihypertensive medications, lipid-lowering medication, anti-diabetic medication, BMI, family history of CHD, diabetes, HDL-cholesterol, total cholesterol, and triglycerides, C-reactive protein and fibrinogen.