Blood carries many hormones that regulate hunger, growth, and other activities. One of these is aldosterone, a hormone secreted by the adrenal gland that, among other things, tells the body to hang on to sodium—which makes you retain water—and excrete potassium. Sometimes the adrenal gland goes wonky and puts out too much aldosterone, causing high blood pressure. Researchers from the National Heart, Lung, and Blood Institute and several hospitals looked at whether levels of aldosterone within a normal range can cause high blood pressure, too.

What the researchers wanted to know: Does the level of aldosterone in your blood influence your risk of developing high blood pressure?

What they did: The researchers used measurements of aldosterone in 1,688 people with normal blood pressure and no heart problems who were getting checked up between 1995 and 1998 as part of the Framingham Offspring Study, a long-term study on cardiovascular disease. The participants were back for another checkup about four years later, between 1998 and 2001, where they had their blood pressure taken as usual. In that time, over a third of the participants' blood pressure had increased markedly, and 250 had developed hypertension (high blood pressure).

What they found: People with higher aldosterone levels to start with had a greater risk of high blood pressure.

What it means to you: This study suggests a possible cause for hypertension in people with no obvious cause.

Caveats: The researchers got aldosterone measurements from one sample of blood at one moment, but it might be more accurate (if much more work) to measure aldosterone over 24 hours in urine. Also, most of the participants were white, so these results may not be true for people of other races.

Find out more: Framingham Offspring Study: http://www.nhlbi.nih.gov/

High blood pressure from the American Heart Association: http://www.americanheart.org/

Read the article: Vasan, R.S. et al. "Serum Aldosterone and the Incidence of Hypertension in Nonhypertensive Persons." New England Journal of Medicine. July 1, 2004, Vol. 351, No. 1, pp. 33–41.

Abstract online: http://content.nejm.org/