Inside Plants: Arginine For Impotence

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On Sundays, my dad and I bicycle thirty miles together. One of our favorite roads runs past a huge sunflower field, and we’ve noticed that the farmers never harvest the seeds. For some unknown reason, they leave the dried flowers standing for the birds to enjoy.

When I mentioned this to Jim Duke, the co-author of this column, he quickly pointed out that not harvesting the seeds is wasteful, in part because sunflower seeds (Helianthus annuus) are the highest plant source of arginine, an essential amino acid that we can only get from our diet or supplements. Arginine supplements are used medicinally for a variety of ailments.

Jim has been particularly interested in arginine because of the recent hype over the impotence drug Viagra (sildenafil). Whenever Jim hears about promotion of a new miracle drug, he immediately starts thinking about which plants might do the same job, only more safely. In his mind, there’s always an herbal ­alternative—whether it’s already known or yet to be discovered.

The advantages of arginine

Impotence often accompanies cardiovascular disease, obesity, diabetes, enlarged prostate, and/or hypertension, and may also be caused by a host of medications that are used to control these conditions.

One of arginine’s functions is to increase our bodies’ production of nitric oxide. Nitric oxide relaxes and dilates blood vessels, promoting better blood circulation to the heart, brain, and bladder. Studies have shown that arginine supplements (1.5 g to 30 g a day) are helpful in treating angina, high cholesterol, hypertension, heart attack, and stroke, which may be because the arginine increases nitric oxide levels. Nitric oxide also relates to sexual function in men. Sexual excitement acts on key pelvic nerves, which call nitric oxide into action—the blood ­vessels expand and the penis becomes engorged, which creates an erection.

Arginine is also needed to increase the output of human growth hormone, which gives us big strong muscles, smooth skin, lean bodies, and lots of energy—like a growing child. Human growth hormone may also play a role in fertility, lowering cholesterol, and improving all the cardiovascular conditions that nitric oxide does.

Arginine sources

Seeds, nuts, and legumes are typically rich in arginine. The highest source by dry weight is sunflower seeds, followed by carob and butternut squash. Other rich sources are sesame seeds, pumpkin seeds, soybeans, peanuts, almonds, watercress, fenugreek, mustard seeds, and Indian figs.

But the research on arginine refers to supplementation with the free amino acid, which is different from how arginine appears in sunflower seeds and other foods. In food, amino acids are linked together by the hundreds or even thousands and must be broken down to be used by the body. In other words, the arginine in sunflower seeds, nuts, and legumes is contained within the structure of the proteins in these foods, so the arginine in these plants can’t replace the synthesized free arginine used in scientific trials. This important distinction is often lost—be cautious if you read something that says otherwise.

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