Normally people discover they're iron deficient during a visit to their GP that was prompted by feeling unusually fatigued. I learned abut my anaemia in slightly more unusual way.

During the production of my new film about mindfulness I had a team of scientists tracking my biological markers as I meditated every day for a year. This included various brain scans, blood tests and saliva analysis. When it came time to reveal my saliva results, we hit an unexpected anomaly; “If your cortisol levels were any lower, you’d probably be dead,” the scientist who was analysing the data told me.

While you might think that low levels of the stress hormone cortisol would be interpreted as a good thing, in this circumstance it was utterly perplexing. The samples had been taken at the start of the project, at a time when my subjective feelings of stress were off the chart. I had insomnia and after having my second child, was struggling to adjust to life as a working mother of two young children. Something wasn’t adding up.

Being an investigative health journalist, I did some further digging and learned that I was in fact anaemic, and it’s probable that my iron and cortisol deficiencies were linked.

Iron is the most common nutritional deficiency in the developed world, affecting around one in three women of reproductive age. And it’s no small thing. We need iron to make hemoglobin, a component of red blood cells that acts like a taxi cab and carries oxygen and carbon dioxide around our body. Aside from making me feel tired, weak and vague, being low in iron could also lead to organ damage. Being low in cortisol is also a concern. Although it is best known for its role in our body’s fight-or-flight stress response, cortisol is also important in metabolism, our immune response, our circadian rhythm and for restoring the balance after a stress response.

My GP immediately prescribed iron supplements and in a matter of weeks I started feeling like I could take on the world with my increased energy.

I’m telling this story to demonstrate the enormous value of nutritional supplementation. But unfortunately it’s not always a good news story. My eyes were opened to the less-than-scientific roots of an inadequately regulated, $133 billion global dietary supplements industry when I read Catherine Price’s book Vitamania.

Like most people, I’d always thought of vitamins and supplements as all-natural, nutritionally sound, quality controlled and rigorously tested wellbeing boosters. I diligently took them as a kind of health insurance policy. If I wanted to prevent myself from getting a cold for example, I’d take vitamin C, envisaging a factory of happy Oompa Loompa's freeze drying thousands of oranges and pressing them into a magic pill that would boost my immune system. But when reading Vitamania, I learned that they’re generally mass produced in factories along with questionable binding agents and fillers. I was stunned when Price revealed that Thiamine, (vitamin B1) comes from a product derived from Coal Tar, that vitamin D comes from lanolin (wool grease), and vitamin A starts with acetone and formaldehyde.

The more I looked into the dietary supplement industry, the more concerned I became. Take Omega 3 for example. As someone diagnosed with an autoimmune disease I’m well aware of the link between Omega 3 deficiency and all manner of immune-related diseases such as cancer, heart disease, Alzheimer’s disease and arthritis.

But researchers are increasingly raising concerns about the chemical integrity of Omega 3 products readily available on store shelves. The oils are highly vulnerable to breakdown during manufacturing and become rancid during transportation and storage. In Canada researchers found that 50 percent of Omega 3 supplements available over the counter exceeded oxidisation safety recommendations. Alarmingly, the products marketed for children with flavoured additives had the highest levels of oxidisation. It’s a similar story in studies that have been conducted in the in South Africa, Australia and New Zealand.

I wish this scenario was limited to Omega 3s. As I’ve written about before, there are also quality concerns with probiotics. As for the ubiquitous multivitamin, studies have consistently found that they provide no clear health benefit. The reality is, we still don’t fully understand the nuances of what vitamins and supplements do in our bodies, how they do it, or what their long-term effects may be. They may actually do more harm than good.

I write these words, not with intention of a making a blanket argument against dietary supplements. I know there’s a good reason they’re called “vitamins” and that “vita” comes from the latin word meaning “life.” In the case of deficiency – think scurvy for lack of vitamin C or thyroid goiters for lack of iodine – they really are vital to human health.

I also know that we live in an imperfect, time-poor world, in which everything from the expense of whole foods, to soil depletion, genetic disposition, gut conditions and chronic stress can cause deficiencies beyond our control. Considering all that we’re up against in modern life, taking a tablet can seem much easier than overhauling other aspects of our diet and lifestyle.

But my point is that a thriving dietary supplement industry has made us think that an isolated single nutrient has the same health effect delivered in a pill as it does when eaten in context of the whole food from which it originated. It conveniently ignores the concept of food synergy, which demonstrates that it’s the whole food, in all its glorious complex composition, that packs the nutritional power punch, rather than single micro food components.

These days I get my anti-inflammatory omega 3 by eating seafood two or three times a week. As for iron, although the supplements have made an enormous difference to my energy levels and a recent blood test showed that my levels are creeping back up, they're also wreaking havoc on my gut and there’s evidence that they may be a quick-fix with long term consequences. Over the next few months I’ll continue taking the supplements while I systematically work with my GP to get to the bottom of my iron deficiency. I’ll also be eating my way to good health by experimenting with my diet until we get things back in balance.