Bilberry extract: night vision myths, eye health claims and safety

Bilberry, Vaccinium myrtillus, grows wild on British heaths and moorland and has darker, juicier fruit than cultivated blueberries. It is rich in anthocyanins and other flavonoids, the pigments that give it its colour. Supplements use fruit extract, leaf extract or both, and a label that does not say which part is used is a poor sign.

A well-known story says that RAF pilots in the Second World War ate bilberry jam to improve night vision. The NCCIH states that the most rigorous studies have not found bilberry effective for improving night vision in healthy people, and says the historical claim likely reflects superstition rather than proven benefit. Marketing that repeats the story is not evidence.

Beyond night vision, bilberry is promoted for tired eyes, diabetic eye disease, macular degeneration and circulation. The NCCIH concludes that bilberry has not been clearly shown to be helpful for any health condition. Its anthocyanins and flavonoids are scientifically interesting, but interesting chemistry is not the same as a proven clinical effect.

For eye health, the proven steps are regular eye tests, not smoking, good control of blood sugar and blood pressure in people with diabetes, and prompt treatment of eye disease. Anyone with diabetes should attend retinal screening whatever supplements they take.

• Sudden loss of vision, a curtain across the vision, new flashes and floaters, or severe eye pain need same-day emergency eye care.

• Gradual changes in night vision should be assessed by an optometrist, as cataract and other conditions are possible causes.

Bilberry fruit is considered safe at amounts normally eaten, and studies used doses up to 160 mg a day for six months without major concerns. Bilberry leaves may be unsafe when consumed in high doses or for long periods of time. Leaf teas and leaf extracts therefore call for more caution than the fruit, and neither should be taken long term without advice.

The NCCIH advises that people on medicines talk to their doctor before using bilberry, because certain herbs and medicines interact harmfully, particularly blood thinners and diabetes medicines. That applies to warfarin, DOACs, aspirin and clopidogrel, and to insulin and tablets such as gliclazide, where an extra glucose-lowering or clotting effect would be unwelcome.

The NHS says herbal medicines can interact with statins, antidepressants, diabetes medicines, blood-pressure medicines, warfarin and hormonal contraceptives, and recommends checking with a pharmacist first. Mention bilberry before surgery as well.

Safety information is limited for pregnancy and breastfeeding, so people should consult a midwife or pharmacist. The NHS does not recommend herbal medicines for children given the lack of safety data. Eating bilberries or bilberry jam as part of a normal diet is a different matter from taking concentrated extract.

Bilberry extracts in the UK are normally food supplements and are not assessed for effectiveness. The Traditional Herbal Registration scheme run by the MHRA gives a mark for registered herbal medicines, representing assessed safety, quality and information but not proven benefit. The MHRA has stated that most herbal medicines on the market are unlicensed and that standards vary, so claims that a supplement treats or prevents an eye disease should be treated sceptically.