This week, international popstar Taylor Swift extolled her words of wisdom in a listicle on the 30 things she learned before turning 30, and it was fascinating.

Writing for Elle US, the ‘Shake it Off’ singer wrote about the breakdown of her infamous ‘girl squad’, her complicated relationship with social media and the one kitchen tool that changed her cooking game (spoiler alert: it’s a garlic crusher.

It was, the supplement Swift uses to “help with” her stress and anxiety that particularly piqued our interests.

“Vitamins make me feel so much better!” she wrote.

“I take L-theanine, which is a natural supplement to help with stress and anxiety. I also take magnesium for muscle health and energy.”

While we're well aware of the benefits of magnesium for improving relaxation and enhancing energy production, we're less familiar with L-theanine. So, to get all the details behind the supplement, we spoke with dietitian Rachel Scoular (Instagram: @healthyhappyhabits) and nutritionist Rebecca Miller of Health With Bec (Instagram: @health_with_bec), and this is what they had to say.

What is L-theanine?

Basically, L-theanine is an amino acid which has been said to help promote feelings of relaxation and relieve feelings of stress and anxiety.

Explaining the science behind the supplement, Scoular says it helps release neurotransmitters throughout the body which "facilitate the creation of alpha waves in the brain." These are the same neurotransmitters we produce during periods of deep meditation and relaxation.

"It is also proposed L-theanine may be linked to regulating bodily responses which may occur during stressful events," she says.

"For example, increased heart rate and stress hormone secretion,  which may possibility link to stress-reducing effects."

According to Miller, effects are generally felt around "30 minutes after consumption" and are said to last for eight to 10 hours when taken at a dosage of 50-200mg.

How can you get L-theanine in your diet?

Here's the good news: if you want to experience the calming effects of L-theanine, the easiest way to incorporate this into your lifestyle is with a good old cup of tea.

However, while white, black and green teas all contain the amino acid, there is some conjecture as to which tea contains the most.

Scoular says green tea has the highest concentration of L-theanine with one cup containing 25 to 60mg, while Miller quotes a 2010 study which states a 200mL cup of green tea only has 4-12 mg, with a cup of black tea containing up to 20-30mg.

Despite this, in order to reach the effective dosage of 50-200mg, synthetic supplements will provide a much higher concentration of the amino acid. In comparison Now Foods, Double Strength L-Theanine capsules contain 200 mg in each capsule, while California Gold Nutrition offers both 100mg and 200 mg potency options.

BUY: Now Foods, Double Strength 200mg L-Theanine Capsules, $20.14 for 60 Capsules OR California Gold Nutrition, 100mg L-Theanine Veggie Capsules, $11.49 for 60 capsules.

Are the benefits and side effects of L-theanine real?

When it comes to the stress and anxiety-relieving side effects Swift shared with Elle, Miller says they have been well-documented, citing a 2016 review of the amino acid which concluded it can assist in "reducing acute stress and anxiety in people experiencing stressful situations".

However, she adds an unfortunate, but important caveat. Miller says that while the supplement "is safe and often beneficial for generalised anxiety," there's currently no "conclusive research," as to what the best dosage is and therefore it's always best to "consult your doctor for guidance" before adding it into your diet.

Scoular agrees, and says while the claims "sound promising," there isn't sufficient and conclusive evidence supporting these statements.

"The majority of research on the action of L-theanine has been conducted in animals, with the need to complete further research on humans to verify these claims," she says.

"For the majority of people, the best way to get a complete range of nutrients is through a well-balanced and colourful diet with plenty of plant-based foods and I strongly suggest you look at changing your diet, before considering supplements.

"You may find benefits from lowering your caffeine intake (as it's a stimulant which activates the stress axis and signals the production of adrenaline) and increasing your intake of antioxidants, which neutralise free radicals and are found in so many fruits and vegetables."

Have you had any experience with the supplement? How do you manage your stress and anxiety? Tell us in a comment below.