Carnitine

Carnitine is one of the better-researched things on the sports shelf, but the effect is still small. These are the questions our naturopaths ask in store, and half of them are about time.

A good fit if

• You're carrying extra weight and you're already changing what you eat and how you move
• You'll give it three months or more rather than judging it after a fortnight
• You train hard and want the long-term approach rather than a pre-workout scoop
• You eat little or no red meat

Check with us first if

• You have kidney problems, especially if you're on dialysis, where muscle weakness has been reported.
• You have a seizure disorder, where seizures have been reported.
• You have metabolic syndrome or known plaque in your carotid (neck) arteries. There's a real warning sign in exactly that group.
• You take valproic acid, phenobarbital, phenytoin or carbamazepine, which lower carnitine themselves.
• You take an antibiotic such as pivampicillin (a pivalate-conjugated antibiotic).
• You're pregnant or breastfeeding, because we have no data either way.
• You're having cancer treatment, because guidelines specifically advise against carnitine then.

• L-Carnitine free base (item 3008). Best known for: The basic form, and the one that does the fat-transport job. Absorption: Raises carnitine in the blood easily. Getting it into muscle is the slow part. Typical use: Body weight and fat mass in overweight and obese adults, and high-intensity exercise performance.
• L-Carnitine L-tartrate (item 3012). Best known for: The usual form in sports products and powders. Absorption: Roughly 68% carnitine by weight, so the label dose and the carnitine dose are not the same number. Typical use: Taken before exercise and for recovery. It is stable and absorbs less moisture from the air than the base form.
• Acetyl-L-carnitine (item 350). Best known for: The form for brain and nerves. Absorption: The acetyl part is itself a building block for acetylcholine (a brain messenger), which is the reason given for this form. Typical use: Studied for nerve and thinking outcomes, mostly in people with diagnosed conditions we can't advertise to.
• Propionyl-L-carnitine (item 4159). Best known for: The form for circulation in the arms and legs. Absorption: Not covered in our sources. Typical use: Its trials are all in people with a diagnosed disease, so the results do not carry over to general use.
• Fumarate, hydrochloride and magnesium citrate salts (items 3009, 3010, 3011). Best known for: Other salts for delivering carnitine. Absorption: We found no evidence specific to these forms. Typical use: Treat them as other ways of delivering L-carnitine. Item 3011 also gives you magnesium.
• D-carnitine or unspecified carnitine. Best known for: The mirror-image form your body does not use. Absorption: Does not apply. Typical use: Not on Schedule 1 and not allowed in listed medicines. No carnitine evidence carries over to it.

Reference values. There's no recommended intake for carnitine. It isn't an essential nutrient for healthy adults, because your body makes it.

Typical supplemental range. Weight trials used 150 mg to 4,000 mg a day over 8 to 30 weeks. Exercise studies used 3 to 4 g just before testing, or 2 to 3 g a day over 4 to 24 weeks. If you're buying the tartrate form, remember it's about 68% carnitine by weight.

Upper level. Not set. There's no upper limit for carnitine, and no carnitine entry on Australia's permitted ingredients list (Schedule 1) has a dose cap. Side effects show up at around 3 g a day.

Worth knowing. Give it months rather than weeks. Muscle carnitine barely changes in a month, and the loading that works seems to need carbohydrate alongside it over 12 to 24 weeks. Take it during the day: one in ten people in a trial had trouble sleeping after a 3 g dose taken 90 minutes before exercise. What you need depends on your age, diet and health, so talk to one of our naturopaths in store.

Food first, where the diet allows it.

• Red meat: by far the richest dietary source
• A vegan diet: supplies almost none, though healthy adults make their own
• Dairy and fish: smaller contributors than red meat

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

• You have metabolic syndrome and existing plaque in your neck (carotid) arteries. A randomised trial found 2 g a day for six months was linked with 9.3% more narrowing than placebo, and bigger rises in total and LDL cholesterol. If this is you, talk to your doctor rather than starting it.
• Long-term use in general. TMAO in the blood rises on 1 to 4 g a day over 12 to 24 weeks, and TMAO is thought to promote artery plaque. Worth knowing, not worth alarm.
• Kidney failure. Muscle weakness has been reported in people with uraemia (a build-up of waste in the blood).
• You have a seizure disorder. Seizures have been reported in people who have one.
• Around 3 g a day and above. Nausea, vomiting, stomach cramps, diarrhoea and a fishy body odour. The odour is the usual reason people stop.
• You take anticonvulsants. Valproic acid, phenobarbital, phenytoin and carbamazepine all lower blood carnitine. That interaction runs from the medicine to the nutrient, and it belongs with your prescriber.
• You take pivalate-linked antibiotics such as pivampicillin. Long-term use can drain carnitine.
• You are having cancer treatment. Professional guidelines specifically discourage acetyl-L-carnitine for preventing nerve damage from chemotherapy, and advise against L-carnitine for cancer-related tiredness.
• Sleep. One in ten people reported trouble sleeping after a single 3 g dose taken 90 minutes before exercise. Take it during the day.
• Pregnancy and breastfeeding. We found no data either way, and Schedule 1 records no warning for any carnitine item. We won't write guidance we don't have.