L-carnitine and heart failure: what the evidence says and UK advice

The NHS describes heart failure as when your heart cannot pump blood properly. It does not mean the heart has stopped working or is about to stop. The NHS says there is no cure, but treatment and lifestyle changes can help, and that treatment aims to ease symptoms and help prevent the condition getting worse. Symptoms include breathlessness, feeling weak or very tired, light-headedness, swelling in the feet, ankles, legs or tummy, sudden weight gain, and coughing at night.

Because living with heart failure can feel like a long-term struggle, many people ask whether a supplement could help the heart muscle make better use of energy. The published analysis of L-carnitine describes it as a vitamin-like, modified amino acid that supports the body's metabolic activities, and that interest in it for heart failure rests on the idea of the failing heart as an engine short of fuel.

The main published summary is a 2017 meta-analysis by researchers in China, which is not UK evidence. It combined 17 randomised controlled trials involving 1625 people with chronic heart failure. L-carnitine treatment was associated with improvements in overall efficacy and in several measures of how the heart works, including left ventricular ejection fraction, stroke volume and cardiac output, and with lower blood levels of the heart failure markers BNP and NT-proBNP.

However, the analysis also found no significant differences in all-cause mortality, in the 6-minute walk test or in adverse events between the L-carnitine and control groups. The authors acknowledged important limitations. The methodological quality of the included studies was less than optimal, so a risk of bias could not be excluded, only 1625 patients were involved, follow-up varied widely from 7 days to 3 years, and doses and manufacturers were not clearly specified in most studies. They concluded that the results were insufficient to recommend it as a first-line treatment or to establish quality of life and long-term results, and that further research was required.

The UK sources read for this guide do not give L-carnitine a role in heart failure care. The NHS heart failure treatment page lists medicines such as diuretics, medicines that widen blood vessels and beta blockers, surgery and devices such as pacemakers, implantable cardioverter defibrillators and left ventricular assist devices, and heart transplant if treatments are not helping, and carnitine is not mentioned. The British Heart Foundation's heart failure information likewise does not mention it.

The BHF's general advice on supplements is cautious. A BHF dietitian says research shows supplements do not help to stop or improve heart and circulatory diseases and that in some cases they can even be harmful. A further BHF page says natural does not always mean safe, that most people do not need supplements unless they have a diagnosed deficiency and that UK Government guidance is that nutritional supplements are not recommended for preventing or managing cardiovascular disease. For another vitamin-like supplement, CoQ10, the BHF says it is not recommended in UK and international heart failure guidelines and is not prescribed by UK doctors, which gives a sense of how supplements are generally treated.

It is also worth saying that no page read for this guide reports a UK recommendation for or against L-carnitine specifically, so the cautious general position is the most reliable guide.

The BHF says supplements can interact with prescribed heart medicines, making treatment less effective or increasing side effects, and that anyone starting a supplement should let their doctor or pharmacist know so they can check whether it is needed and safe alongside prescribed medication. The pooled analysis reported no significant difference in adverse events for L-carnitine in the trials it examined, but the trials were short and varied in design, so this is not a guarantee of safety in every situation.

Heart failure treatment usually involves several medicines, kidney and blood tests and regular review. A supplement that affects any of these may complicate care, so mention it at appointments in the same way as any medicine.

Talk to your heart failure nurse, GP or cardiologist before starting. They can tell you whether your medicines are optimised, which supplements, if any, make sense given your kidney function and other treatment, and whether you are eligible for something with a firmer evidence base, such as cardiac rehabilitation or device therapy. The NHS says to see a GP if you have symptoms of heart failure, to ask for an urgent appointment or NHS 111 help if you feel breathless when lying down or from everyday activity, are coughing up frothy pink phlegm or have suddenly gained weight, and to call 999 if you have severe difficulty breathing or someone has passed out and is not responding normally.

Do not stop or swap prescribed heart failure medicines in favour of a supplement.

Heart failure is diagnosed and managed through GPs, heart failure nurses and cardiology teams on the NHS, with blood tests, an ECG and scans such as an echocardiogram. Supplements, including L-carnitine, are bought privately as food supplements and are not NHS-prescribed for heart failure. Whatever you buy, make sure the team looking after you has an up-to-date list.