Vitamin D: How to Maintain Optimal Levels Year-Round (#14)
Vitamin D is a crucial yet often underestimated factor for health and performance, especially for those of us living in northern latitudes. This article explores how vitamin D impacts the body, why deficiency is so common, and its implications for you as an athlete. Although the body can produce Vitamin D through sunlight, it's not sufficient during much of the year, leading many to have levels that are too low. The conclusion is clear: it's not about getting a performance boost, but about avoiding limitations. Ensuring adequate levels year-round is a fundamental requirement for training, recovery, and optimal performance.
What is Vitamin D?
Where does Vitamin D come from?
You probably already know that we produce vitamin D ourselves when the sun's rays hit our skin. However, during certain months, which we'll discuss later in the article, it's nearly impossible for us in the north to produce vitamin D from the sun. Instead, we need to focus on the vitamin D we obtain from our diet.
From our diet, we get both vitamin D2 (ergocalciferol) and D3 (cholecalciferol). D3 primarily comes from animal sources such as eggs, fatty fish, and shellfish. Vitamin D2 is mostly found in plants, particularly mushrooms and algae. Unfortunately, vitamin D2 is not the body's preferred form; it favors the D3 variant. D3 is also the form we produce ourselves from sun exposure.
Vitamin D Deficiency
Here are some of the most typical factors influencing the occurrence of deficiency
- Latitude
- Skin color
- Weather
- Sunscreen
- Age (older people synthesize less efficiently)
- Environment/air pollution
- Behavioral patterns and social factors
No matter what we discuss, there's rarely a single reason for something to happen, and the same goes for vitamin D deficiency. The main factor often discussed is our latitude and the fact that between October and March, we Nordics can essentially not produce vitamin D from the sun. The sun's UVB rays are far too weak for this to be effective.
The Athlete's Specific Needs
Aren't summer rays and vitamins from food enough?
Sure, but it requires exposure — something we're generally not great at. If we look at our neighboring country Estonia, a healthy diet and the sun aren't sufficient for most people. During the winter months, 73 percent have insufficient levels, and during the summer, there's still 29 percent not reaching healthy levels of vitamin D. Jumping over to Finland, they recommend vitamin D supplements for everyone up to the age of 18.
In our latitudes, we basically get no vitamin D from the sun between October and March, which accounts for six out of the year's twelve months. Moreover, it's essentially only between 11 a.m. and 5 p.m. that we can benefit from the sun's rays. It's basically set up for us to miss the sun in today's society when most of us work indoors during the day.
How can you tell if you're getting enough?
The only certain way is through blood tests, but if you don't regularly visit the hospital, here's some helpful research and statistics that might give you an idea.
In a newly published review study, a research team led by Veugler compiled results from 108 studies involving 13,987 participants. The findings show that it takes about 3000 International Units (IU) to reach a blood plasma level of vitamin D at 50 nmol/l. That number might not mean much without some context, but 50 nmol/l is the threshold for "health," indicating a healthy level we should aim for in our blood. Anything below 25 nmol/l is considered a deficiency.
So how can you improve performance with Vitamin D?
Can it become toxic?
It's clear that there's a toxic threshold for vitamin D, just like with anything else. Some people have taken excessively high amounts, between 30,000–50,000 IU per day over the course of a year, leading to dangerously elevated levels. However, this concerns a systematic, massive intake over a prolonged period.
An intriguing study from 2014 examined how seasonal changes influenced vitamin D levels among a group of 32 people living at our latitude, specifically in line with southern Denmark, N54 latitude. The researchers discovered that most participants had insufficient vitamin D levels during winter (63 percent of the group). Interestingly, a greater decline in vitamin D levels was linked with diminished working memory and decision-making skills. The actual levels are significant, but maintaining stable levels over time is also, if possible, another crucial factor for mental health.