Asparagus is not only a tasty seasonal treat but also has intriguing health effects.
ANSWER: Along with the first flush of spring blossom comes one of the great vegetable treats of the season: asparagus. Asparagus spears are typically in the shops only from September to December, ensuring the arrival of this tasty vegetable is greeted with gusto. And as well as being delicious, it has intriguing health effects.
Asparagus is high in folate content, ranking alongside such stars as broccoli and spinach. It also contains antioxidants such as vitamin C and carotenoids, along with other vitamins, minerals and fibre, making it one of the more beneficial vegetables.
A major 2014 review published in the British Medical Journal involving nearly 470,000 study participants noted a higher intake of fruit and vegetables was linked to a lower risk of all-cause mortality, but particularly death from cardiovascular disease. On average, each additional serving of fruit and vegetables a day reduced mortality risk by about 5%.
There are many possible mechanisms by which vegetables decrease our risk of disease. For a start, they can prevent the oxidation of cholesterol and other lipids in the arteries, potentially halting their progression to atherosclerosis or heart disease. The same heart-health-promoting antioxidants also relax the blood vessels and stop the clumping together of blood platelets that can lead to clots.
But the benefits of asparagus may go further. It has compounds that also help regulate blood pressure and therefore reduce hypertension risk, a major factor in cardiovascular disease.
Blood pressure is controlled by the renin-angiotensin system (RAS), which acts on fluid and electrolyte balance, among other things. A key regulator is angiotensin-converting enzyme (ACE), which constricts arterial vessels, in the process raising blood pressure when required by the RAS.
People with high blood pressure are sometimes given so-called ACE inhibitors to reduce the enzyme’s constricting effect and bring the pressure down. Protein sources such as casein and tuna, along with many plant foods, have been found to contain peptides that are ACE inhibitors.
In one study, researchers measured levels of inhibitory activity and the amount of known ACE inhibitor nicotianamine in 80 vegetables, including asparagus. Asparagus was found to have a significant inhibitory effect despite having a small amount of nicotianamine, suggesting it contains some other blood-pressure-lowering compound.
Japanese researchers may have identified the magical chemical in a 2013 rat study. A sample of rats with hypertension were fed either a standard diet or a diet containing 5% asparagus – some of it from New Zealand – for 10 weeks.
The asparagus-fed rodents were found to have significantly lower systolic blood pressure and ACE activity. This led the researchers to a compound in asparagus called 2”-hydroxynicotianamine, which they concluded was a potential factor in lowering blood pressure.
Clearly, we are not rats, so although the Japanese experiment is interesting, it can’t be considered definitive. Nonetheless, large trials involving humans have also shown that increased consumption of fruit and vegetables can contribute to a small decrease in blood pressure.
Whatever future research reveals on the specifics of asparagus and cardiovascular health, we already know that the vegetable is a rich source of several important nutrients and fibre.
Ultimately, however, the best vegetable for you is the vegetable you will eat. If you love the taste of asparagus, then make the most of the season.
This article was first published in the October 19, 2019 issue of the New Zealand Listener.