1.   ...naturally occurring substances which the body can convert into vitamins.

2.   Arsenic, a naturally occurring substance, is also a known carcinogen.

3.   Beta carotene is a naturally occurring substance in fruits and vegetables that is converted to vitamin A in the body.

4.   A. Pectin is a naturally occurring water-soluble substance that is found in some ripe fruits like apples and plums, especially in the skins and seeds.

5.   Creatine is a naturally occurring substance in food.

6.   EPO is short for erythropoetin, a naturally occurring substance that stimulates the production of red blood cells.

7.   For men who suffer from impotence, Viagra blocks an enzyme that breaks down a naturally occurring substance that causes erections, Sabanegh said.

8.   Stroke specialists are especially heartened by the findings because inosine is a naturally occurring substance with no obvious side effects.

9.   Svanborg and her team hope that because HAMLET is a naturally occurring substance, it might not be toxic like so many other cancer drugs.

10.   The issue is complicated because testosterone is a naturally occurring substance and it is difficult to tell when it has been introduced externally.