By David Holden, ND, MS, Naturopathic Physician & Nutritional Biochemist
I know — you've heard me say this before. And I'm going to keep saying it until more of you finally take it on board. Because every winter, the same thing happens: people come into my clinic feeling run-down, foggy, and miserable from colds and flu that were entirely preventable.
After four decades of clinical practice, I can tell you with complete confidence: immunity doesn't happen by accident. It's built — deliberately, systematically, and well before the cold months arrive.
The good news? It's not complicated. Here are what I call the Big Five — the foundational immune essentials I recommend to every patient, every year, when the temperature starts to drop.
Zinc is one of the most under-dosed nutrients in the Western diet, and one of the most critical for immune function. I recommend Sanderson's or Clinicians brand — either tablet or liquid form.
Here's what most people miss: the dose on the bottle isn't enough. Aim for 1–2 tablets daily with food, or 6–10 drops of liquid zinc diluted in juice (not water — it tastes awful on its own). Men generally need a slightly higher dose than women.
Zinc is involved in hundreds of enzymatic reactions in the body. Without adequate levels, your immune system is simply working with one hand tied behind its back.
Vitamin D3 is at least as important as Vitamin C when it comes to preventing winter illness — yet most adults in New Zealand are chronically deficient, especially coming out of winter. The key is that you must always pair it with K2, which helps your body actually use the D3 effectively and prevents the calcium dysregulation that can otherwise occur.
My protocol: 5,000 IU of D3/K2 daily through summer and the warmer months; double that — 10,000 IU — through winter, split across morning and evening.
Start as soon as it gets consistently cooler (think early May in New Zealand) and maintain through until spring — roughly early October when we're regularly seeing days over 20 degrees. For children under 40 kg, halve the adult dose; for smaller children under 25 kg, reduce to a third.
The reason most people's immunity collapses in winter isn't a mystery. Their vitamin D3 levels have dropped, and they haven't done anything about it.
Standard powdered or tablet Vitamin C has its place, but if you really want to supercharge your immune system, liposomal (lypo-spheric) Vitamin C liquid is in a different league entirely — absorbed up to ten times more efficiently than conventional forms.
I recommend the Clinicians Liquid Lypo C with Quercetin. The Quercetin is a bonus — it helps keep airways clear and has meaningful cardiovascular benefits as well.
Adults should aim for a minimum of 3–5 grams daily, spread across the day. This is not a one-big-hit-in-the-morning situation — the body works best when you maintain steady tissue saturation throughout the day. Less than this, and you're unlikely to get the immune activation you're after.
Avoid the cheap liposomal sachets — the chemical stabilisers make them taste unpleasant and reduce their efficacy. Go for quality. Your immune system will know the difference.
This isn't fashionable nutritional advice. It's biochemistry, backed by more than 50 years of research. Sugar depletes B vitamins, magnesium, and a cascade of other minerals — exactly the nutrients your immune system depends on.
Every time you (or your kids) consume a fizzy drink, a processed snack, or refined sugar in any form, you're actively undermining your immune defences. It's that direct.
I'm not asking anyone to be perfect. But becoming genuinely aware of how much hidden sugar you're consuming — particularly through processed foods and drinks — is one of the highest-return changes you can make to your immune resilience. Not next month. Now.
This sounds obvious, yet it's consistently under-prioritised. Your immune system is built from what you eat. Full stop.
Quality proteins (grass-fed meats, eggs, legumes), healthy fats (avocado, olive oil, oily fish, nuts), and a generous variety of vegetables give your body the raw materials it needs to build and maintain a robust immune response. These aren't just "health foods" — they are the structural components of your immune cells, your hormones, and your cellular repair machinery.
For those of us in our fifties, sixties and beyond, this matters even more. The body's ability to synthesise and absorb nutrients becomes less efficient with age — which means the quality of what you put in needs to go up, not down.
This is the foundation of what I now call Biohacking — the deliberate use of nutrition, lifestyle, and targeted supplementation to optimise how your body functions at every age. It's not just for elite athletes. It's for anyone who wants to feel genuinely well, maintain their strength and sharpness, and age on their own terms.
While not strictly one of the Big Five, I want to mention this because it's so consistently overlooked: probiotic foods are often more effective — and far cheaper — than probiotic supplements.
A good quality supplement has its place, but if you're looking for sustained gut immune support, rotating real probiotic foods into your daily diet is where to start. Sauerkraut, non-dairy kefir, kimchi, and coconut yoghurt are your friends here. One of these, daily, makes a meaningful difference to gut flora diversity and immune resilience.
(A note: I'd steer clear of kombucha unless you're making it yourself and can control the sugar content — commercial versions tend to be far too high in sugar to be genuinely beneficial.)
Here's the thing most people don't appreciate: meaningful immune resilience doesn't happen overnight. For adults under 40, you're looking at several weeks to build up adequate levels of these key nutrients. For those of us over 60, it can take several months. This is why starting now — at the beginning of the cooler season — is so important, rather than waiting until you're already sick.
Prevention is always easier than recovery.
The Big Five are a powerful foundation. But optimal immunity and resilience — especially as we age — involves a more personalised picture. Your individual biochemistry, health history, stress levels, sleep quality, and existing nutritional status all shape what your body actually needs.
If you'd like a fully tailored immunity and resilience programme, I'd encourage you to book a consultation with me directly. Over 40 years of clinical practice in nutritional biochemistry and natural medicine means I can assess exactly where your immune system is underperforming — and precisely what to do about it.
To arrange a consultation with David Holden, contact Holden Health Care:
🌐 www.HoldenHealthCare.com
David Holden is a Naturopathic Physician and Nutritional Biochemist with over 40 years of clinical experience. He is a pioneer in dark field live blood microscopy and evidence-based natural medicine in New Zealand.
