How about a sweetener that is 100 percent natural and contains zero calories?

Think you've fallen down the rabbit hole?

Stevia is just that. It's a leafy green plant, native to South America, that can serve as a substitute for sugar. Botanically, it's related to ragweed and the daisy, and has been used by indigenous peoples medicinally for centuries.

Although you can buy whole leaves of stevia in some of the finer grocery stores, it's more commonly sold – and more conveniently used – in liquid extract or powder form. But be careful: it is 200 times sweeter than sugar in the same concentration.

There are two principal compounds that are extracted from stevia that bring all the sweetness. Known as stevioside and rebaudioside A, these extracts have been clinically studied so that scientists can better understand the plant's medicinal properties. The scientists have not been disappointed.

In a randomized, double-blind, placebo-controlled trial in 174 Chinese patients over two years, the systolic and diastolic blood pressure of the stevia group dropped considerably. They also had a lower risk of left ventricular hypertrophy, an enlarging of the heart that can be caused by elevated blood pressure.

What's the science? It's still only a theory, but some researchers believe that stevioside may act by blocking calcium ion channels in cell membranes, a mechanism similar to some blood pressure lowering drugs.

The last disease you would expect a sweetener like stevia to be useful against would be diabetes, and you would be wrong. A Danish team of scientists found that diabetics who took stevioside had a reduction in blood sugar by about 18 percent.

How does this work? Additional tests in mice and rats indicate that stevioside may increase production of insulin, as well as make the cells more sensitive to its effects.

The list goes on and on: scientists have learned that stevia may help prevent heart disease by lowering oxidized LDL cholesterol. Other tests have proven the sweetener's anti-inflammatory, anti-cancer, diuretic and immunomodulatory super powers.

One note: the amounts of stevia used in these tests and trials are well beyond what you would be stirring into your afternoon tea. But given alternatives like sugar, which will slowly kill you, or some of the more dubious sugar substitutes, which may do the job even faster, it's a delight to know there is a natural sweetener that is also healthful, even to a small degree.