Taken from a site called life-enhancement.com. I know they are selling products but their magazine has fascinating articles!
"These data are consistent with the work of pioneering cardiovascular surgeon Dr. James Isaacs, of Baltimore, who tested the hypothesis that supplementing with natural thyroid extract could help prevent cardiovascular disease.3 According to his classic study, conducted in 1974, people who took 1/4 grain of thyroid along with vitamins and minerals over a period of 10 years showed significant improvement in cardiovascular function, regardless of whether they were slightly hyperthyroid, slightly hypothyroid, or had normal thyroid function.
Famed alternative physician Dr. Jonathan Wright recommends his whole-thyroid formulation, containing the same amount of thyroid used in the Isaacs study, for people over age 40 who have no overt endocrine disease. He points out that, even if one is not experiencing overt symptoms of low thyroid, all endocrine glands are beginning to slow down at this stage of life. The most common comment from people taking 1/4 grain of his natural thyroid extract, according to Dr. Wright, is, "I just feel a little more energetic overall. My thinking seems a little clearer, and my bowel function is a little better."
Yet another study has recently pointed in the same direction. Last year a French study involving 1434 healthy male patients with no known history of thyroid disease and with normal levels of thyroid-stimulating hormone found that patients with lower levels of the thyroid hormone thyroxine had more cardiovascular risk factors and were therefore more likely to develop atherosclerosis and other forms of cardiovascular disease.4
Even if someone is already taking thyroid supplementation, most can still add a thyroid nutritional supplement to get the benefits of the other glandular extracts that it may contain, according to Dr. Wright. "Unless you are in very brittle condition - and brittle means to an endocrinologist that the amount you take has to be exactly right - you might consider the use of a thyroid supplement, if it adds only a modest amount of the actual thyroid glandular itself, and if it also nourishes the rest of the endocrine network."