Last year, in a report on hypertension, or high blood pressure, the American Heart Association stated that there was no definitive evidence that it did. However, the report was not able to state definitively that it did not.
The status appeared to be that, simply, no reliable studies appeared to have been done on the subject.
The study actually was not specifically aimed at the question of yoga, per se, as a way to lower blood pressure, but, was concerned with various “alternative” methods of managing hypertension. While the study did not generate its own data through testing, it instead, defined through large amounts of data and reached its conclusions based on the results of several other studies.
This should not be taken as a specific denunciation of yoga as a blood pressure lowering tactic in itself.
Here's my unscientific take on the subject.
It has long been accepted that regular, moderate exercise can help lower blood pressure. Yoga is a form of exercise, and, if done properly and regularly, produces at least the same results of other forms of exercise.
Among these benefits are better functioning of all parts of the body, a tendency to indulge in additional activities beneficial to health (proper nutrition, rest, and a willingness to participate in other physical activities).
Of course, if someone purely makes a basic yoga routine without guidance two or three times a week, as with other forms of exercise, they will get out a result related to the amount of effort they put in. However, if someone really takes their yoga practice to heart, they will begin to experience physical results at a higher level. Additionally, immersing oneself more deeply in a yoga practice tend to lead to other lifestyle changes which can produce health benefits, including, reducing hypertension.
Lifestyle changes, and benefits, often associated with yoga include better nutrition, lower stress, and a meditative state.
Again, a regular practice of yoga does produce a meditative state, and often leads to the practice of yoga itself, which has been linked to lower stress, and lower blood pressure. Yoga and meditation both have been shown to reduce stress, which even by itself, can help lower blood pressure.
Also, yoga as exercise, together with proper nutrition can help with weight loss, or at least weight management, and maintaining a healthy weight can also help keep blood pressure at lower levels.
So, while there seems to be no direct evidence that yoga is a good way to manage hypertension, the total package of health benefits of a regular yoga practice make it worth your while to consider. Of course, in an area as important, and as potentially dangerous as high blood pressure, you should consult medical experts before relying on any alternative method of keeping this important measurement under control.