Vitamin D
Vitamin D is often lumped in with other nutrients, but it’s not technically a vitamin. It behaves more like a hormone and plays a crucial role in many processes—especially those involving your immune system and thyroid.
Getting enough vitamin D from food alone is next to impossible. If you have thyroid issues, fatigue, or autoimmune concerns, low vitamin D might be part of the picture.
The Thyroid Connection
Low vitamin D levels are strongly associated with higher TSH (thyroid stimulating hormone), which can be a red flag for underactive thyroid function. Several studies have shown that optimising vitamin D can improve TSH levels and may enhance the efficacy of thyroid hormone replacement in people who are already on it.
Even more importantly, vitamin D is one of the key immune-regulating nutrients. This matters if you have—or are at risk of developing—Hashimoto’s or other forms of autoimmune thyroid disease. Ensuring optimal levels (not just “within range”) has been shown to reduce antibody levels and support immune regulation.
So Why Are So Many People Low?
Vitamin D is known as the “sunshine vitamin” because your skin synthesises it in response to UVB light. But here’s the catch—your ability to make enough depends on:
Latitude (how far south you live)
Time spent outdoors
Skin exposure (arms and legs—not just your face)
Sunscreen use
Time of year
Age, skin tone, and even gut health
It’s no surprise that vitamin D deficiency is common, especially through the winter months or in people who avoid direct sun exposure.
I see borderline or low levels all the time, especially in clients who are burnt out, inflamed, or managing thyroid or immune challenges.
Can You Get It from Food?
Not easily.
Cod liver oil is one of the most concentrated sources, but you’d need a large daily dose to meet basic requirements.
Oily fish like salmon, sardines, and mackerel contain more vitamin D than most foods and also support thyroid function with selenium and iodine.
Egg yolks offer a small amount, but not enough to move the needle for most people.
Mushrooms grown under UV light can contain significant vitamin D, but the levels vary wildly depending on how they’re cultivated. Exposing white button mushrooms to natural sunlight or a UVB lamp can boost their D2 content dramatically. One study found just one second of UV exposure raised levels to over 800% of the RDI.
Even with a great diet, food alone is rarely enough to get you to optimal levels.
Testing & Supplementing: What You Need to Know
You can ask your GP for a vitamin D blood test, but in some cases, you may need to self-request or pay privately. I recommend testing for anyone with:
Thyroid or adrenal symptoms
Autoimmune conditions
Mood disorders or fatigue
Poor immune resilience (e.g. frequent illness, slow recovery)
In New Zealand, optimal levels tend to sit between 100–150 nmol/L, not just above the deficiency cut-off.
Depending on your levels, sun exposure may help maintain vitamin D in summer months, but supplementation is often needed—especially through winter.
My Recommendation
If you’re tired of guessing what your body needs and want to take a more strategic approach to your health, it’s time to get tested, get clarity, and get a personalised plan.
You don’t need to figure it all out alone.
I help women uncover the root causes behind their symptoms and create simple, tailored plans that work with their body—not against it.
Here’s how we can work together → Work With Me
Want to learn more about some of the other top nutrients that support thyroid health? Start here:
