Bio Synergy 5000iu is the UK’s highest-strength Vitamin D3 supplement for an improved immune system. If you often feel tired, have sore muscles, weakness, hair loss or even mood changes including depression, this can be a sign of a dietary deficiency in Vitamin D (for details of studies head to PubMed and National Institute of Health). Those most at risk of a Vitamin D deficiency include those with darker complexion, vegans, vegetarians and those who spend a lack of time outdoors among others. Studies, have proven that daily supplementation with a high-quality Vitamin D supplement will help to tackle this, making this powerful pack of 90 capsules a must-have for anyone who may be deficient.