Rule 1 Citrulline

L-citrulline is straightforward once you know what it's been tested for. These are the questions our naturopaths ask in store.

A good fit if

• You're middle-aged or older and blood vessel health is why you're looking
• You want a clean single-ingredient powder where the label dose is the dose
• You're happy with a small, average effect rather than a guaranteed one

Check with us first if

• You take blood pressure medicine, nitrates or sildenafil-type medicines. There are no interaction studies, and citrulline acts on the same blood vessel signal.
• You plan to take it with L-arginine, which lowered blood pressure much more in older adults than citrulline on its own.
• You're combining it with several other pre-workout ingredients before very long, hard sessions.

• L-citrulline (pure). Best known for: The weight on the label is the citrulline dose, and it's the form used in blood vessel trials. Absorption: Gets past the breakdown in the gut and liver that limits oral arginine, and raises blood arginine. Typical use: 3 g a day in blood vessel trials in older adults, and 8 g a day over 6 weeks in one gym trial.
• Citrulline malate. Best known for: Citrulline bonded to malic acid, and the form in most gym trials. Absorption: Same pathway. A 6-week trial found no difference from L-citrulline in nitric oxide markers. Typical use: 6 to 8 g of powder before training, which is only about 4 to 5.3 g of citrulline.
• L-arginine. Best known for: The amino acid citrulline turns into. Absorption: Mostly broken down in the gut and liver when swallowed, so it's a poor way to raise blood arginine. Typical use: Only allowed in listed medicines applied to the skin in Australia, not oral ones.
• Watermelon. Best known for: The best-known food source. Absorption: Not described in our sources. Typical use: Didn't improve artery widening in trials. It's a food, not a measured dose.

Reference values. There's no NRV or RDI. Your body makes citrulline, so it isn't an essential nutrient.

Typical supplemental range. Blood vessel trials in middle-aged and older adults mostly used 3 g of L-citrulline a day, taken daily for up to 12 weeks. Gym trials used about 5.3 g in a single dose before training, and 8 g a day over 6 weeks.

Upper level. An Australian listed medicine can't provide more than 6 g of citrulline a day. No scientific Upper Level has been set, because there isn't enough safety data for amino acids like this one to set one.

Worth knowing. With L-citrulline, the grams on the label are the grams of citrulline, so there's no ratio to work out. The 8 g a day gym trial is above the Australian 6 g cap, so a listed medicine can't give you that dose. What you need depends on your age, diet and health, so talk to one of our naturopaths.

Food first, where the diet allows it.

• Watermelon: the richest known food source. A reliable amount per serve wasn't available in our sources

If any of these sound like you, talk to one of our naturopaths or your doctor before you start.

• You take blood pressure medicines, nitrates or PDE5 inhibitors such as sildenafil. There's no interaction study, but citrulline works through nitric oxide and lowered blood pressure in older adults, so an added effect is plausible. Check with your doctor or pharmacist.
• You're combining it with L-arginine. The pair lowered systolic blood pressure by about 10 mmHg in older adults, far more than either alone, which matters if you take blood pressure medicine.
• You're pregnant. It's only been trialled under specialist supervision for specific conditions, so no general safety conclusion can be drawn. We don't recommend it.
• You're breastfeeding. There's no data at all, so we don't recommend it.
• Children and teenagers. It's only been studied in hospital and disease settings, and adult doses haven't been studied in them.
• You combine heavy supplement stacks with extreme training. There's one case of exercise-induced muscle breakdown (rhabdomyolysis) on a multi-ingredient stack including 10 g of citrulline malate, though it wasn't put down to the citrulline.
• Dose. An Australian listed medicine can't provide more than 6 g of citrulline a day, and there's no scientific Upper Level.