Boosting your immune system - orange

Over the winter months, many of your patients will turn to multivitimins in an effort to improve immunity and ward off winter viruses. 

It can be a consumer mind field to determine fact from the marketing hype. As supplements contribute to polypharmacy for older patients and those with chronic illness, it’s an opportune time to discuss what will provide benefit and alternative options.

Vitamin C, D and Zinc are three supplements commonly selected by consumers over the winter months so let’s examine the role of these supplements and possible dietary alternatives.

  • Vitamin C

    For decades vitamin C has been hailed as a prevention and treatment of cold and flu symptoms. Many studies have looked at this area but the evidence for supplementation is not strong. A Cochrane review from 2013(1) was consistent with earlier reviews stating that regular supplementation with vitamin C does not reduce the incidence of contracting the common cold. Evidence for taking vitamin C as a cold treatment shows mixed reviews, some showing no difference while others studies show symptoms abating about half a day earlier. While vitamin C is a relatively safe supplement and low cost, individuals may wish to test their tolerance to short term supplementation. However given that long term supplementation is not providing additional benefit then encouraging vitamin C rich foods as a baseline immune booster over supplements is better practice. Great food sources of vitamin C available in season during winter include: broccoli, brussel sprouts, oranges, kiwifruit and grapefruit that can be included as part of the recommended daily 2 serves of fruit and 5 serves of vegetables.

  • Zinc 

    Taking oral zinc supplements during a cold, has been shown to reduce the longevity on average by 1-1.5 days but not the severity of symptoms(2). For the best results zinc needs to be commenced within 24 hours of onset of symptoms but commonly has a side effect of bad taste and nausea. There is not currently strong evidence for prophylactic zinc supplementation for prevention of colds in adults. The RDI for zinc is 8mg for women and 14 mg for men, this is easily achievable through diet with our major protein foods (lean meats and dairy, legumes and lentils) being significant sources of zinc. Current guidelines recommend 2-3 serves of protein foods and 2-4 serves of dairy foods be consumed per day.

  • Vitamin D 

    In Australia 30-50% of adults are vitamin D deficient and vitamin D levels are known to drop by 10-20nmol/L over winter(3). With sunlight Australia’s major source of vitamin D, many people struggle to get enough over the colder months. Our food sources in Australia are very limited with most adults only obtaining only 5-10% of their requirements through food. While the links with Vitamin D and bone health have been recognised for some time now, a review published earlier this year shows vitamin D supplementation to be protective against acute respiratory infections(4). For those with vitamin D deficiency or who spend most of their daylight hours indoors, consider a vitamin D supplement regime. 


Author: Ms Denise Burbidge (BND, APD, GCDE), Accredited Practising Dietitian. Denise works in clinics across Melbourne (click here for locations) and has a special interest in diabetes, gastrointestinal nutrition and nutrition support for older adults.



(1)    Hemilä H1, Chalker E.(2013) Vitamin C for preventing and treating the common cold. Cochrane Database Syst Rev. Jan 31;(1):CD000980. doi: 10.1002/14651858.CD000980.pub4.

(2)    G. Michael Allan, MD and Bruce Arroll, MB ChB PhD (2014) Prevention and treatment of the common cold: making sense of the evidence CMAJ. 2014 Feb 18; 186(3): 190–199. doi:  10.1503/cmaj.121442

(3)    Nowson et al (2012). Vitamin D and health in adults in Australia and New Zealand: a position statement. MJA 196(11)

(4)    Martineau et al (2017) Vitamin D supplementation to prevent acute respiratory tract infections: systematic review and meta-analysis of individual participant data. BMJ 356:i6583. Doi:10.1136/bmj.i6583