NO: Another reason to say yes to vegetables

A new study highlights the potential benefits of higher habitual dietary nitrate, predominantly from vegetables, to support muscle function in adults independent of physical activity levels.

Dietary nitrate, a bioactive compound found primarily in green leafy vegetables and beetroot, has been found to improve skeletal muscle function. More specifically, dietary nitrate enhances nitric oxide (NO) bioavailability, which is a gaseous signaling molecule that is thought to improve blood flow to skeletal muscle. NO also triggers smooth muscle relaxation and vasodilation of blood vessels.  In 2018, the International Olympic Committee classified nitrate supplements as an ergogenic aid for athletes.

To examine if habitual dietary nitrate intake was associated with better muscle function in a large cohort of men and women with ages ranging across the adult lifespan, Marc Sim (Institute for Nutrition Research, School of Medical and Health Sciences, Edith Cowan University) and colleagues analyzed data from the Australian Diabetes, Obesity, and Lifestyle Study. This national population-based survey recruited Australian adults (25 – 85 years of age) in 1999/2000 with follow-up in 2004/2005 and 2011/2012.  To assess dietary nitrate intake, the researchers used a food-frequency questionnaire that was administered at these 3 time points over the 12- year period. Objective measures of muscle function, which were obtained during 2011/2012, included isometric muscle strength of the lower limbs and tests of mobility.

Cutoff-points for weak knee extension strength (kg) for men aged < 65 y and > 65 y were 25.1 and 18.4 kg, respectively.  Using the same age criteria, the cutoff-point for weak knee extension strength (kg) for women was 15.1 and 10.3 kg, respectively. Mobility was assessed using the 8ft timed-up-and-go test (s), which captures functional activities of daily living such as sitting, standing, walking, and turning. The cutoff-points for slow 8ft-TUG were 6.25 and 8.00 s, for those < 65 y and > 65 y respectively. Individuals with the highest nitrate intake had between 31%-37% lower odds for presenting with poor muscle function measures compared to those with the lowest nitrate intake.

This study, published in The Journal of Nutrition, provides evidence for the long-term benefits of higher habitual nitrate intake obtained predominately from vegetables (approximately 90 mg/d; typically provided from 1 cup of green leafy varieties) for muscle function in men and women of various ages. Considering that poor muscle function is linked to adverse clinical outcomes such as injurious falls, a diet with an abundance of nitrate-rich vegetables could be a novel strategy to promote muscle function.

Public health messages should continue to encourage higher vegetable intake, while highlighting the importance of nitrate-rich vegetables, such as green-leafy vegetables and beetroot, for musculoskeletal health to facilitate healthy aging.   A corresponding editorial by Brandon Yates and Andrew Coggan (Indiana University) suggest that these novel findings may be beneficial for maintenance of muscle function over time, especially in aging adults who suffer from physical function impairments.

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