Researchers from Japan recently published a meta-analysis of clinical trials and cross-sectional observational studies of a vegetarian diet and blood pressure (BP) (42). Many of these vegetarians were semi-vegetarians.

Among seven clinical trials, a vegetarian diet was found to reduce systolic and diastolic blood pressure by an average of 4.8 and 2.2 mm Hg, respectively. Among the 32 cross-sectional studies, vegetarians were found to have a lower systolic and diastolic blood pressure of 6.9 and 4.7 mm Hg respectively. These findings were statistically significant.

The authors said, “According to Whelton et al, a reduction in systolic BP of 5 mm Hg would be expected to result in a 7%, 9%, and 14% overall reduction in mortality due to all causes, coronary heart disease, and stroke, respectively….Obesity, excessive sodium intake, and excessive alcohol use are associated with increased BP and risk of hypertension; potassium intake and physical activity are associated with lower BP. In addition, intake of unsaturated fat, protein, magnesium, and dietary fiber may be associated with differences in BP.”

Interestingly, the only clinical trial that showed a vegetarian diet to increase blood pressure was the first PCRM pilot study using a vegan diet to treat type 2 diabetes (2). Diastolic blood pressure did decrease more in the control group, than the vegan group, in that study, while those on the vegan diet ended up with lower systolic blood pressure. However, two of the five subjects on the vegan diet who were on blood pressure medication discontinued their medication, while only one of four in the control group discontinued.

I have updated the Blood Pressure section of Disease Markers of Vegetarians

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References

1. Yokoyama Y, Nishimura K, Barnard ND, Takegami M, Watanabe M, Sekikawa A, Okamura T, Miyamoto Y. Vegetarian Diets and Blood Pressure: A Meta-analysis. JAMA Intern Med. 2014 Feb 24. | link

2. Nicholson AS, Sklar M, Barnard ND, Gore S, Sullivan R, Browning S. Toward improved management of NIDDM: A randomized, controlled, pilot intervention using a lowfat, vegetarian diet. Prev Med. 1999 Aug;29(2):87-91. | link

Following up on the post, White Blood Cells in Vegans, I came across two more pieces of info.

The Linus Pauling Institute says, “Vitamin A and retinoic acid play a central role in the development and differentiation of white blood cells, such as lymphocytes, which play critical roles in the immune response (1).”

Unlike omnivores, vegans do not have a direct, dietary source of vitamin A, but rather get it indirectly via carotenoids (mainly beta-carotene). Beta-carotene is fat-soluble. It seems theoretically, possible then, that a low intake of carotenoids or fat could contribute to lower vitamin A status and white blood cell count (WBC).

This is purely hypothetical; to my knowledge vitamin A levels have not been measured in vegans and other signs of low vitamin A status have not been a noted problem. Anecdotally, I had been eating plenty of beta-carotene and fat at the last measurement of my WBC which showed them to be below normal.

Paul Appleby, of EPIC, passed on a study to me of a clinical trial using a “Daniel Fast” from the University of Memphis (2). In this trial, mostly healthy and some vegetarian subjects (13 men, 30 women; 20-62 years old) went on a Daniel Fast for 21 days, eating no processed or packaged food and only plant foods (as much as they wanted). Their WBC went from an average of 5.7 to 5.0 (2). 5.0 is within the normal range, but on the lower end (normal being about 3.5 to 12.5 billion per liter).

The authors of the Daniel Fast study say, “It has been suggested that ingestion of food additives and preservatives can increase white blood cell count by triggering an immune response due to a sensing of invading pathogens from the food stuff; however, we are unaware of any scientific reports that confirm this hypothesis.” I should point out that lots of things have been suggested, but it doesn’t seem impossible that vegans generally eat less food additives and preservatives and this could be contributing to low WBC.

I have added this information to VeganHealth’s article on White Blood Cells.

There were some other interesting things about this study. Here are the before and after (or during in the case of the nutrient intakes):

calories: 2,185 → 1,722
fat (g): 74 → 54
fat (%): 30 → 27
saturated fat (g): 24 → 9
cholesterol (mg/dl): 171 → 139
LDL (mg/dl): 98 → 76
weight (lbs): 171 → 167
bp: 115/72 → 106/67

The authors did an analysis which showed that the improvements in these parameters did not occur in only the unhealthier subjects, but rather across the board. They say, “It is interesting to note that even those subjects who were vegetarian prior to starting the fast experienced dramatic reductions in total and LDL-[cholesterol], in addition to improvements in other markers. Clearly, the exclusion of meat from the diet (as is the case for vegetarians) is not the only dietary factor involved in raising circulating cholesterol and other risk factors for cardiovascular and metabolic disease.”

It should be noted that this trial had no control group and was not randomized in any way.

I found this interesting because even though the subjects didn’t lose much weight (the weight change wasn’t even statistically significant), their blood pressure and cholesterol levels went down substantially in only 3 weeks. That’s impressive. But does it mean that it is the diet that everyone should be on all the time, indefinitely?

Stay tuned.

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Reference

1. Linus Pauling Institute. Micronutrient Information Center. Vitamin A. Accessed 5/20/13 | link

2. Bloomer RJ, Kabir MM, Canale RE, Trepanowski JF, Marshall KE, Farney TM, Hammond KG. Effect of a 21 day Daniel Fast on metabolic and cardiovascular disease risk factors in men and women. Lipids Health Dis. 2010 Sep 3;9:94. | link

In 2009, preliminary cross-sectional data on blood pressure rates among various diet groups were reported from Adventist Health Study 2. Just today, a more thorough report was posted at PubMed. The 2012 report only included whites and the results did not appear to be adjusted. But, in any case, vegans had a 63% reduced risk of having high blood pressure, as compared to regular meat-eaters, which was highly statistically significant. Lacto-ovo vegetarians had a 43% reduced rate, which was also statistically significant. More details can be seen in Table 12 of Disease Markers of Vegetarians at VeganHealth.org.

Body mass index was able to account for most of the differences in blood pressure between the diet groups, though other factors probably play a small role, such as higher potassium and lower sodium intakes, and lower insulin levels and blood viscosity.

Reference

Pettersen BJ, Anousheh R, Fan J, Jaceldo-Siegl K, Fraser GE. Vegetarian diets and blood pressure among white subjects: results from the Adventist Health Study-2 (AHS-2). Public Health Nutr. 2012 Jan 10:1-8. [Epub ahead of print] Link