Zinc. Not the kind that protected Chris Pringle as the New Zealand cricket team won their way through the nineties, but the inorganic mineral that is somewhat lacking in our food supply. Close to a quarter of New Zealand adults aren’t getting an adequate intake, according to the National Nutrition Survey. Men over the age of 50 are at most risk, with more than 50 per cent reporting inadequate intakes, and a staggering 90 per cent of men over 70 not reaching the target.
Zinc is one of those nutrients that doesn’t get much airtime, so fewer people are aware of issues associated with deficiency. It is one of the first things people might take when they have a cold or flu — and in fact one of the initial signs of zinc deficiency is a depressed immune system, as it plays an important regulatory role in the production and signalling of important inflammatory cytokines.
However, this is just the tip of the iceberg when it comes to functions that zinc performs. It is second to calcium as the most abundant metal in the human body, serving as a co-factor for more than 300 enzymes that drive physiological functions, including energy metabolism, cell division, genetic expression, cognitive function and neurotransmitter production.
When lecturing about zinc, I always refer to its importance in wound healing, ulcers and male fertility and reproduction, given it has a critical role in testosterone production. There is ten times more zinc in the cells of the prostate gland than in any other tissue, and there is an association between an enlarged prostate gland and low zinc levels in the blood, even at a moderate deficiency.
Zinc is involved in fertility in women too, helping with the efficient use and metabolism of oestrogen and progesterone. Sub-optimal zinc levels are associated with higher oestrogen levels, an impairment in ovulation and subsequent infertility.
Cardiovascular disease and diabetes are two of the most burgeoning health problems society is experiencing, and though the focus is often on macronutrient intake (i.e. carbohydrate, protein and fat), micronutrients are just as important in the prevention or progression of these conditions.
The underlying cause of these chronic diseases begins with inflammation and it’s no surprise that low zinc levels are associated both with the build-up of plaque on the arteries and insulin resistance. Clinical studies have found that zinc helps stimulate the production of hormones that regulate appetite, fat storage and glucose uptake in the body — these are all processes that are compromised in an inflamed state. In people with diabetes, there is an increased risk of nerve damage and end-stage kidney disease with low serum zinc levels.
It’s not just that our intakes are low, but there can be a double whammy effect with our digestion. Zinc plays an important role in the production of stomach acid, low levels of which will reduce our ability to digest and absorb all nutrients and delay gastric emptying. Reflux can occur when carbohydrates begin to ferment in the gut. This can help explain the prevalence of sub-optimal zinc status among people with gut inflammation and digestive issues. The lack of stomach acid will contribute to increased inflammation, thus increasing zinc requirements and quite likely increasing the amount of zinc we lose, given that 85 per cent of zinc losses are through the small intestine.
The association between zinc and mental health has also been studied, due to its role in the production of seratonin, one of our “feel-good” neurotransmitters, which is produced in the gut. In fact, the three days’ post-partum period where new mothers may experience depression has been linked to low levels of zinc during pregnancy.
Why do we have zinc deficiency?
Firstly in New Zealand our soil is depleted in minerals such as zinc, and therefore vegetable sources are lower than they were in the past. This is problematic when combined with the plant-based movement where many people believe it is healthier to consume a mostly vegetarian diet.
Indeed, this is reflected by data showing a reduction in zinc consumption from the last National Nutrition Survey in 1997. Yes, you know I’m a massive fan of vegetables! But it’s not correct that a vegetarian diet is “healthier”.
The most bioavailable form of zinc in our diet is from protein: oysters have 70mg zinc per 100g; beef and lamb come a distant second with around 12mg per 100g. Seeds and nuts contain between 5-10mg per 100g depending on type (pumpkin seeds are one of the richest sources) and spinach and mushrooms have approximately 1mg per 100g, and — much like bread and pasta, from which New Zealanders get a substantial amount of their zinc — these plant-based sources are poorly absorbed compared to oysters, beef and lamb, due to the anti-nutrients such as phytic acid present in the food.
How much zinc do you need?
If you aren’t lucky enough to enjoy oysters on a regular basis, and aren’t consuming that much red meat, how do you know if you need to eat more? If you are vegetarian, should you be supplementing?
As a guide we should be consuming between 8-11mg of zinc per day, easily met by eating 100g of beef or lamb. Try the beef and pumpkin curry sprinkled with pumpkin seeds just before serving. Vegetarians may like to serve roast pumpkin, pumpkin seeds and feta on top of lightly steamed spinach with added chickpeas.
My best recommendation is to ask for a blood test from your doctor to establish your serum zinc level. Bear in mind that even if you fall within the “normal” part of reference ranges, there may be reason to increase zinc intake, particularly if you are experiencing any of the health conditions I’ve mentioned (among others). If low or low “normal”, work with a qualified nutritionist or dietitian to optimise zinc intake through diet or supplementation.