Ask the doctor: I take a lot of daily supplements. Should I reduce it to an all-in-one tablet?

​Dr Grant replies: In short, these expensive heavily marketed online multivitamin subscriptions have limited (if any) clinical data supporting their ‘superior’ efficacy, so I recommend you keep your money in your bank account.

Continue as you are, but make sure you are not overdosing and like I always say, get the basics right first. We are lucky to live in resource-rich countries and have access to healthy nutritious food daily. Aim for 2-3 portions of low sugar fruit per day such as berries, mandarin oranges, apples or nectarines. Aim for up to five portions of vegetables per day (ideally at all meal times, otherwise you may not hit your target) and add some green leafy vegetables daily. There is insufficient evidence that vitamin supplementation can prevent disease in most healthy adults on a normal diet (not vegan or vegetarian) even if they have low serum levels of vitamins during routine blood testing. Low levels may not reflect actual deficiency.

There is no doubt that vitamin D plays a role in calcium and bone homeostasis, and potentially regulates many cellular and immune functions. This is why it has been suggested that taking a vitamin D supplement may help prevent some cancers and promote immune system function. The reality is that more scientific data is needed. A causal relationship has not been established between poor vitamin D status and major diseases such as autoimmune disorders, cardiovascular, and metabolic diseases.​

Certainly, expectant or lactating females, postmenopausal females and patients with osteoporosis should take calcium and vitamin D supplements. Be mindful of not taking too much — the upper limit for vitamin D is 4000 units daily for healthy adults. Fat-soluble vitamins (vitamins A, D, E, and K) are generally more toxic than water-soluble vitamins. Vitamin A, if taken during pregnancy, is teratogenic (toxic to the growing foetus) at doses with an apparent upper threshold at 10,000 units daily. Expectant females should always stick to the pregnancy-approved multivitamins.

There is no evidence that regular vitamin C supplementation reduces the incidence of the common cold but taking it when suffering with a common cold may reduce the duration of symptoms. Medical conditions that may reduce the absorption of vitamins include bariatric surgery for weight loss, Coeliac disease or Crohn’s disease. Patients with excessive alcohol consumption, and chronic use of certain medication may also need to increase certain vitamin requirements. Older adults or patients living in long term care facilities should consider daily supplements as the absorption of vitamins declines with age and the diet may not contain enough fruit, vegetables and leafy greens.

I always caution patients who take iron supplements, due to the risk of iron overload and the potential for the genetic condition haemochromatosis. Unless you are following a vegan diet, when low dose iron may be required, or you are suffering with heavy menstrual periods and had low iron stores during blood testing, there is generally no need to take iron supplements.

Lastly, omega 3 supplements, particularly EPA (EicosaPentaenoic Acid), and DHA (DocosaHexaenoic Acid) as major active ingredients in omega 3 supplements are safe and may have potential cardiovascular and metabolic benefits. They need to be taken daily in fairly high doses for weeks to months before any potential health benefits are seen. The US FDA (Food and Drug Administration) advises the general population not to exceed 3g/day of EPA and DHA combined, with up to 2g/day from dietary supplements.

Dr Jennifer Grant is a GP with Beacon HealthCheck