Do I Still Need to take Vit D in the Summer? 🧐
Why I'm supplementing, even with the sun out 🌞
The most glorious season is finally upon us - ahhh, Summer!
There's arguably nothing better than the feeling of the warm sun on our skin, bare feet in the grass, fresh air filling our lungs.
One of the reasons sunshine feels so good? It’s not just our mood - it’s our biophysiology.
When our skin is exposed to UVB rays, we actually synthesize a powerful hormone-like nutrient: Vitamin D.
If you aren’t already in love with this power-player, then buckle up and prepare your heart; this nutrient is about so much more than just bone health.
Let’s dive in…
Vitamin D receptors can be found throughout the entire body - in nearly every major tissue and cell type - including the brain, heart, immune cells and reproductive organs. When we consider this widespread presence of Vitamin D receptors (VDR) we can begin to get a sense of why sufficient levels of Vitamin D are so important, affecting critical functions like immune regulation, hormone signaling, gene expression, brain and mood, even fertility.
It is currently estimated that 70% of the people in the U.S. have a Vitamin D deficiency while over 40% of the global population are deficient.* Take a minute to let that set in - that is MA 👏🏼 JOR 👏🏼.
What’s more: Vitamin D deficiency is an under-appreciated problem for those trying to regulate their weight as Vitamin D plays an essential role in the regulation of blood glucose and insulin levels which are integral to maintaining a healthy weight.
According to a 2025 report from the Harvard Gazette, a report published in The American Journal of Clinical Nutrition found that adults supplementing with 2,000 IU/day of Vitamin D3 over four years experienced significantly less telomere shortening - the cellular marker of aging - compared to those taking a placebo. In fact, the difference was equivalent to preventing nearly three years of biological aging. (Source: Harvard Gazette, May 2025)**
Harvard, you had me at telomere protection! But before we all go sprinting to the supplement aisles, let’s discuss supplement type because this is where it pays to be picky. You heard it here last: not all supplements are created equal.
So where to start? Let’s first select which form. The form I’m looking for when selecting a Vit D supplement is cholecalciferol. It’s the active, bioavailable form we want to ensure the body is able to utilize what we’re giving it. (There is also a D2 form found in some plants but it is less effective than D3 and not naturally made in the human body).
Next we want to consider what it is paired with: enter our friend K2.
We can think of Vitamin D as the nutrient that helps us absorb calcium - and K2 as the nutrient that tells our bodies where to put it. Without enough K2, calcium can end up in the wrong places (think: arteries, soft tissue), rather than in our bones and teeth where we want it. K2 effectively acts as the dutiful traffic director, and pairing it with D3 ensures the body can make use of it safely and effectively.
TLDR; Vitamin D3 helps the calcium get in, K2 tells it where to go.
And don’t forget the fat.
Vitamin D is fat-soluble, meaning your body absorbs it best when it’s taken with a source of fat. Can you imagine spending time, money and energy to take these supplements only to have them pass right through you?! Ugh, so sad.
Fortunately for us, many Vit D3K2 supplements come already prepared in MCT or coconut oil so you don’t need to worry about consuming fat alongside your supplements for optimal absorption.
So, back to our initial question: Is it necessary to supplement Vitamin D in the summer?
Perhaps where you live you get ample Vitamin D directly synthesized from the sun, and if that is you, I’m green with envy! But the truth is that many of us spend quite a bit of time indoors or maybe we can’t get the amount of direct sun we need before we burn (which I am not advocating for, but that is a separate conversation). Most of us, myself included, can significantly benefit in myriad ways from immune support to glucose regulation to longevity from the simple supplementation of Vitamin D, D3 with K2 to be precise.
The recent release of the above cited Harvard study helped solidify my decision; anything protecting my telomeres - Vitamin D supplementation is for me year-round!
(telomeres are the protective caps at the ends of chromosomes that shorten during aging and are linked to the development of certain diseases.)
And did you notice that the data collected in the Harvard study was over four years? This is a key data point; we cannot commit to our health and expect things to change immediately and then claim “we’ve tried everything” when we are trying to reverse decades of sub-par nutrition or poor habits. That’s not to induce shame, just a reminder that we are in this for the long-game. Our bodies are the only home we get for this life, and in my opinion, investing in our health is one of the best investments we can make!
For a peek as my Wellness Essential supplement List, including the Vitamin D3 K2 supplement I take personally and recommend to my clients, click the link below. You will also get access to 10% off sitewide through Fullscript for any other supplements you purchase!
Ready to take back your health and reclaim your vitality?! Or simply looking to review your supplement protocol? I’d love to chat! Click the link below to schedule a FREE 20 minute consult 👇🏼
xoxo.
Gretchen
* Source: The Ultimate Guide to Vitamin D, Shawn Wells, MPH, LDN, RD, FISSN, CISSN. shawnwell.com
**It is important to note the Recommended Daily Allowances as determined by the National Academy of Medicine are 600IU/day for Children aged 1 - Adults aged 70 (including pregnant and breastfeeding women), and 800IU/day for adults aged 70+. My intention with this article is to show how recent research and studies are indicating a more substantial supplementation approach to be advantageous. Always consult your doctor or healthcare provider before taking a new supplement.