As the UK swelters through a prolonged heatwave in August 2025, health experts are urging caution with certain dietary supplements that could pose risks during hot weather. Belle Amatt, a registered nutrition consultant at W-Wellness, highlights specific supplements that may increase skin sensitivity to sunlight or interact with other substances, potentially causing adverse reactions during summer months.
Supplements to approach with caution.
- St John’s Wort can heighten skin sensitivity to UV light, increasing the risk of sunburn, redness, itching, and rashes.
- High-dose Vitamin B6, typically above 100 mg daily, may also increase UV sensitivity, though this is less common.
- Prescription retinoids, used for conditions like acne or psoriasis, significantly elevate photosensitivity, requiring strict sun protection measures.
- Vitamin D supplementation remains safe and often necessary, with toxicity rare below the UK’s 4,000 IU daily limit.
Amatt advises: “During the summer months, it is wise to avoid supplements that increase skin sensitivity to UV light. St John’s Wort is a notable example, as it can make the skin more prone to sunburn and irritation.” She adds that high-dose Vitamin B6, while less risky, should be moderated unless medically necessary, as it has been linked to increased UV sensitivity at doses around 100 mg daily or higher.
For those prescribed retinoids, Amatt stresses, “High-dose retinoids, prescribed by healthcare professionals primarily for skin conditions like acne or psoriasis, are known to increase photosensitivity and sunburn risk. Anyone prescribed retinoids should follow their GP or dermatologist’s advice on sun protection rigorously during treatment.” Unlike over-the-counter vitamin A supplements, these pharmaceutical treatments demand careful management during sunny weather.
Vitamin D, however, remains a safe option for most. Amatt notes: “Moderate Vitamin D supplementation is safe during summer and often necessary since many people do not get enough sun exposure due to indoor lifestyles, sunscreen use, skin tone, or geography. Toxicity is rare and typically associated with very high doses over time, well above the UK’s upper limit of 4,000 IU daily.” Regular testing can ensure levels remain optimal without over-supplementation.
Potential reactions from risky supplements
Photosensitising supplements like St John’s Wort can trigger adverse skin reactions. “Supplements that increase photosensitivity, such as St John’s Wort, can cause adverse skin reactions including redness, itching, rashes, and sunburn following UV exposure,” Amatt explains. High doses of Vitamin B6 may occasionally contribute to similar effects, though these are less frequently reported. These risks underscore the need for careful supplement choices during heatwaves, when UV exposure is often higher.
Interactions with food and drink
Some supplements can interact with dietary components, affecting their efficacy or absorption. Amatt warns, “High doses of minerals like calcium may reduce the uptake of certain nutrients. St John’s Wort is known for multiple interactions that can affect how other substances are metabolized.” She recommends, “Paying attention to timing and dietary context helps optimise absorption and minimise unwanted interactions. Consulting a qualified Nutritionist when taking supplements is a wise way to ensure that you are taking them safely and effectively.”
Safer alternatives for summer
For those seeking mood or energy support typically provided by St John’s Wort, Amatt suggests alternatives like valerian or Californian poppy. “For mood or energy support often sought with St John’s Wort, herbal alternatives such as valerian or Californian poppy may be considered. These herbs are traditionally used to promote relaxation and improve sleep without known photosensitizing effects,” she says. She also recommends Artah Sleep Tonic, which combines these herbs for a safe, relaxation-promoting option.
Amatt advocates a holistic approach: “Complementing herbal options with lifestyle approaches – regular exercise, good sleep hygiene, and stress management – offers a holistic and safer strategy, especially during the summer months.” This advice aligns with guidance from the NHS, which encourages balanced lifestyles to support overall health during seasonal changes.
As heatwaves intensify UV exposure, choosing supplements wisely is critical. Consulting healthcare professionals and nutritionists can ensure safe supplementation, protecting health while enjoying the summer sun.