The Vitamin D Danger: When Supplements Go Too Far

The Vitamin D Danger: When Supplements Go Too Far / Alessandra Edwards

In Australia, we’re living a paradox worthy of a medical sitcom: blessed with endless sunshine, yet somehow managing to be vitamin D deficient. It’s like having a bank account that’s perpetually empty despite winning the lottery. How did we get here? Well, the story starts with some traumatised British children and their cod liver oil…

From Fish Oil to Phone Apps: A Century of Progress?

The story of vitamin D starts with one of medicine’s less appetising chapters. Before the 1850s, coastal communities in England, Holland, and France had a particularly stomach-turning folk remedy: cod liver oil produced by, well, letting fish livers rot in barrels until they produced a yellow, creamy oil. Yes, you read that correctly—rotting fish liver juice was considered medicine.

Thankfully, by 1853, someone finally thought “there must be a better way” and invented steam-based extraction. Suddenly, what was essentially fishermen’s garbage became a global health commodity, shipped from Norway to Hamburg, London, and New York as a miracle cure for physical fortification.

By the 1920s, mothers across Britain were waging a daily battle: spoon-feeding their protesting children this marginally less revolting version of cod liver oil. If you’re old enough to remember this culinary torture, I apologise for triggering your gag reflex. These mothers didn’t know why it worked, just that it kept rickets at bay. In 1922, biochemist Elmer McCollum finally identified the magical ingredient: vitamin D, proving that sometimes the worst-tasting medicine really does work.

The Aussie Sunshine Paradox: Too Much, Yet Not Enough

Here’s our uniquely Australian challenge: we live in one of the sunniest countries on Earth, yet over 50% of Victorians are vitamin D deficient during winter. We’ve become so good at ‘slip, slop, slap’ that we’re practically wearing hazmat suits to check the mail. Our vitamin D levels are paying the price for our sun-safety success.

The irony deepens: UV levels have increased by 2-6% since the 1990s, and melanoma diagnoses are projected to rise by 24% over the next decade. We’re caught in a peculiar balancing act between getting enough vitamin D and avoiding skin cancer. It’s like trying to toast marshmallows without burning them—possible, but requiring more finesse than you’d expect.

The Modern Food Plot Twist

Our struggle with vitamin D isn’t just about sun exposure. Our food sources have changed dramatically too. Our great-grandparents got their vitamin D from organ meats, fish eggs, and eggs from chickens that actually saw the sun.

Today?

Let’s just say those battery-farmed chickens aren’t working on their tans. Modern eggs contain about 75% less vitamin D than their pasture-raised ancestors. That’s some serious nutrient inflation—you’d need to eat four modern eggs to get the same vitamin D as one egg your grandmother ate.

When Good Intentions Go Too Far

This is where many of us reach for supplements, and this is where our problems begin. A century after cod liver oil, we’ve swapped the fishy spoonful for sophisticated supplements, but we might have overcorrected.

As a health scientist, I’m watching an alarming trend: people popping vitamin D pills like they’re candy, without any testing or monitoring. It’s like replacing a precision instrument with a sledgehammer. Unlike most vitamins that you simply excrete if you take too much, vitamin D is fat-soluble, meaning it can accumulate in your body over time. 

While you can’t “overdose” on sunshine (thanks to your body’s natural off-switch), you can definitely overdo it with supplements.

Excess vitamin D isn’t just a waste of money— it’s potentially dangerous. 

Too much can lead to calcium building up in your blood (contributing to atherosclerosis), cause kidney problems, interfere with heart function, and ironically, create the very bone problems you’re trying to prevent.

Understanding Your Body’s Vitamin D System

Your body handles vitamin D with impressive sophistication—when it comes from sunlight, that is. Think of your skin as having a built-in safety system: it simply stops making vitamin D when you’ve had enough. But supplements bypass this system entirely.

When we test vitamin D levels, here’s what we’re looking for:

  1. 50-125 nmol/L is your sweet spot (though some scientists argue that 50-75 nmol/L is optimal).
  2. Above 150 nmol/L? Time to ease off.
  3. Above 250 nmol/L? Step away from those supplements!

Interestingly, there’s a growing hypothesis that our century-long love affair with vitamin D supplementation might have unexpected consequences. Some researchers suggest that the rise in allergies, including hayfever, could be linked to widespread vitamin D supplementation over the past 100 years. While this research is still emerging, it’s another reminder that more isn’t always better when it comes to nutrients.

The Supporting Cast

And if you still decide to go ahead and supplement, please be aware that vitamin D needs backup to do its job properly. It’s not just about getting enough vitamin D—it’s about getting the right mix of nutrients:

– Magnesium is crucial in vitamin D metabolism (and unsurprisingly, most people I test are low in it).

– Vitamin K2 helps direct calcium to your bones instead of your arteries (where you definitely don’t want it).

– You need enough calcium in your diet, or vitamin D might start borrowing it from your bones.

Another interesting fact is that extra body fat can trap vitamin D, making it less available for use (People living with obesity or who are overweight often show lower vitamin D levels because the nutrient gets stored away in fat tissue rather than circulating in the bloodstream where it’s needed).

Smart Solutions for the Sunburnt Country

So how do we get this right? 

  • Get tested before supplementing.
  • Download two sun apps:
    The free SunSmart Global UV App tells you exactly when to apply sun protection based on your location. I love this app and I got my kids to install it on their phone so I no longer have to answer the daily question of whether they need to apply sunscreen.
    For vitamin D specifically, the DMinder app acts like a personal sun coach, complete with a stopwatch feature to help you hit your targets without overdoing it.
  • Consider the supporting cast (vitamins need friends too).
  • If supplementing, start moderate (1000-2000 IU daily for most adults).

From cod liver oil to sun apps, we’ve come a long way in our vitamin D journey.

The good news? You no longer need to traumatise your taste buds to get your daily dose.

The bad news? You’ll need to be smarter about it than simply overdosing on supplements.

But hey, at least you’re not drinking rancid fish oil.