Your Vitamin D Is About As High Right Now As It Gets All Soccer Season

Most of what I work on with soccer players involves what's on their plate and in their cup. Vitamin D works differently. Your body makes it in your skin, out of sunlight, so this one runs on a calendar. Fall is the part of the calendar where the number is usually near its high point.

That matters as timing more than as a random trivia fact. Everyone's vitamin D is worth looking at this season and fall is a reasonable time to bring it up with a physician.

None of what we're going to be discussing is an emergency and none of it is a reason to buy anything today. It is a reason to ask one question at an appointment you are already going to.

What the seasonal pattern actually looks like in competitive athletes

The clearest picture I have seen in a competitive population comes from a 2020 study in the Journal of Nutritional Science, which followed 47 university athletes in the United Kingdom. Researchers measured the same athletes twice, once in autumn and once in spring. The group's average vitamin D fell from 52.8 nmol/L to 31.0 nmol/L, and the change was statistically significant.

Two things about that matter. It is a group average, and individual athletes in that study sat all over the range, so a group mean says nothing certain about any one person. It is also a UK cohort, so the size of the swing is impacted depending on where you live.

The mechanism is why the calendar matters. Skin production is driven by sunlight exposure, which is not evenly available across the day or the year. Research on skin synthesis has found that very little vitamin D3 gets made before 10 in the morning or after 3 in the afternoon. That is during summer. Through winter, especially those living further north and away from the equator, very little if any gets made at all. A related US-specific estimate puts that line at about Fayetteville, North Carolina, and Albuquerque, New Mexico for those who love geography and want to map it out.

That is a long way of saying that your 6:30 PM soccer practice in November is doing a great many good things for you. Vitamin D production though is not one of them.

How common is low vitamin D in soccer players

Common enough to be worth a conversation, and the honest number comes with conditions attached.

One of the most detailed soccer-specific measurement in the research I reviewed comes from a 2025 study in Translational Sports Medicine. Among 209 young academy players aged 7 to 18, measured in February, 38.3% were insufficient and a further 26.8% were deficient. That puts roughly two thirds of those players below what we'd like to see at a minimum.

Both of those conditions push a prevalence figure up. February is the low point of the seasonal curve and the location was particular far north meaning the sun exposure and impact was very minimal.

That is where the honest answer stops. No study I found measured below-sufficiency prevalence in soccer players living further south. What the research does establish is that location moves this a great deal. The same 1988 work that found no vitamin D produced in Boston skin from November through February found that at further south locations, sunlight still produced it in the middle of winter. Location clearly matters.

The supplement half that soccer academy was already taking

The most useful part of this topic comes from those same 209 soccer players.

More than half of them, 52.6 percent, reported taking vitamin D on their own. When the researchers measured everyone's blood, the two groups were statistically indistinguishable. Players taking something and players taking nothing came back with no significant difference between them. And across the whole group of 209, in 84.2 percent of cases, which is 176 players, the athlete or whoever bought the supplement could not say what dose it was.

I want to be careful about what that does and does not show. It is a snapshot of one squad at one moment, so it describes what was true in that room without explaining why. There was no discussion about how consistent they were with taking the vitamin D either which is a very big factor. It is a long way from evidence that vitamin D supplements do nothing and I've seen enough first hand to believe and feel confident in the opposite.

What it does show is that buying something and knowing it is working are two different things. In this squad, the buying happened far more often than the knowing.

One thing to note as well is that adding more vitamin D on top of an already adequate level has not produced a measurable performance gain in different studies. Correcting an actual shortfall is a different question and the literature treats it separately. That is where many effects/benefits really show up.

Where the evidence is thinner than the headlines suggest

You will find vitamin D credited with better strength and fewer illnesses. I would like the evidence to be that tidy but it is a little messier than that.

On muscle, the largest trial-level review available, which explicitly excluded athletes, pooled 54 randomized controlled trials across 8,747 people. It found no benefit to muscle health, alongside a statistically significant worsening on a functional mobility test and on knee flexion strength. The authors' own inclusion criteria read: studies in humans, except athletes. So it is at once the strongest trial evidence on muscle and the least transferable to you.

On illness, a small trial in male taekwondo athletes who were vitamin D insufficient reported that supplementation may reduce upper respiratory symptoms during winter training. It's always difficult to tell how much something does directly impact the frequency of getting sick or for how long that sickness lasts but the mechanism of vitamin D does show it can have benefit/impact on it.

The case for paying attention to vitamin D does not rest on any of that. We continue to learn more and more as study after study comes out supporting areas in which vitamin D could be beneficial so if you do find out you are deficient I would strongly encourage prioritizing getting those levels up.

What food and sunlight can and cannot do

Very few foods naturally contain vitamin D. Fatty fish like salmon, tuna and mackerel are among the best natural sources, and fortified foods, milk especially when fortified with vitamin D, provide most of the vitamin D in American diets. So your plate is doing real work here. That work though many times does come up a bit short of the total amount many of us need daily.

What it cannot do in particular is quietly replace a winter's worth of missing sunlight. A fortified breakfast covers a small fraction of what clinicians use as a reference intake for someone short on sun. Diet is a meaningful contributor and a poor substitute for correction.

On sun, no source gives a number of minutes, and I would be suspicious of anyone who does. Location, season, cloud cover, the hour of the day and the person all change the answer. The research describes a window of hours and stops there.

The timeline is the real argument for doing this in the fall

If your level does come back low, correcting it runs on weeks and months. Clinical guidance commonly puts a recheck around eight weeks after starting, and if the level has not come up by then, another eight-week course after that. The source I am drawing on states plainly that the optimal recheck point has not been clearly defined. Everybody responds differently. Dose, how low the starting point was, body composition and absorption all move the timeline.

Now run that forward from two starting dates.

Start in September. A physician decides whether a test makes sense, the test happens, a result comes back, and if something needs correcting the recheck lands in late fall. Whatever the answer is, it arrives with the season in front of it.

Start the same conversation in January and the same sequence puts the recheck in March, with a second stretch running toward May. For most soccer calendars that is the back half of the season, or past it.

The seasonal data makes this sharper. In that same UK study of 47 athletes, 34 percent were classed as deficient at the spring draw, using the UK threshold of below 25 nmol/L. Spring is the low point, so a high figure there is what the pattern predicts. A test run at the bottom of the curve tells you about the bottom of the curve.

Nothing about this moves fast, and that is the whole reason it is worth raising early.

Why nobody may have mentioned it at your last physical

A specific thing athletes run into: bloodwork comes back normal, nobody says the words vitamin D, and everyone assumes it was covered.

Vitamin D status has its own test and it is not automatically part of a routine panel. Current guidance supports testing on individual risk factors rather than screening everybody, so it tends to get ordered when something specifically suggests ordering it. A normal panel confirms what was on the panel.

The published risk profile is what that guidance is built on. In athletes, the factors named include being under 18, lean body mass, winter and early spring seasons, and living further north. One analysis found athletes measured in winter or spring were almost twice as likely to be short, and said the same of athletes living further north. If you are a teenager playing club or high school soccer in the northern half of the United States, you check more than one of those boxes.

That is a reason to ask a question. The guidance the profile comes from says directly that it is not a reason to test every athlete.

What to actually do with this

One thing at a time.

Pick one appointment you are already going to this fall. Ask whether 25-hydroxyvitamin D has ever been run, and if so, when the sample was drawn, because the season changes how a result reads. That question costs nothing.

If you are already taking something, find out the dose and what it is aiming at. If nobody in the house can answer that, sort it out before a

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Frequently Asked Questions

Should every soccer player get their vitamin D tested this fall?

No blanket recommendation exists. Current guidance points toward risk-based testing rather than screening everybody. Fall is a reasonable time to raise the question, particularly for athletes carrying several of the known risk factors, and the decision belongs with the clinician. Personally I don't think knowledge is ever a bad thing and testing can be beneficial for everyone to just know where they stand.

What is a normal vitamin D level?

Authorities differ, which is worth knowing before you read a lab report. Sufficiency is set somewhere in the range of roughly 20 to 30 ng/mL depending on the organization, and no single cutoff is universally correct. For optimal levels in athletes I generally like to see those levels at 40 ng/mL.

Can I just start a supplement without getting tested first?

Testing first is preferable, because dosing decisions are individualized and clinician-directed. The academy study above is the practical argument. Half that squad reported supplementing, most could not name a dose, and their bloodwork looked no different from the players taking nothing.

Does this apply if I live somewhere sunny?

The seasonal logic is strongest where winter meaningfully cuts outdoor sun exposure, and further south the pattern is likely less pronounced. That is different from saying it does not apply, and the low-latitude evidence in soccer players is thin.

How do I know if my nutrition is actually the problem?

That is the harder question, and it is rarely about one nutrient. If you have been flat through the back half of a soccer season, sleeping fine and training hard with nothing to show for it, the fueling side is worth a proper look before anything narrows to a single test. That is what a free 15-minute Discovery Call is for.

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If nobody has looked at the whole picture for you, what is on your plate, what is in the cupboard, and what has actually been measured, a free 15-minute Discovery Call is where we start.  Book Your Discovery Call

Jay Short, MS, RD, CSSD is a Registered Dietitian and Board Certified Specialist in Sports Dietetics, and co-owner of Rise Nutrition, specializing in sports dietetics for competitive athletes. He works with US Soccer (all 27 teams), the Columbus Blue Jackets (NHL), and athletes across MLS, collegiate, and club programs.

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References

1. Wilson-Barnes SL, Hunt JEA, Williams EL, Allison SJ, Wild JJ, Wainwright J, Lanham-New SA, Manders RJF. "Seasonal variation in vitamin D status, bone health and athletic performance in competitive university student athletes: a longitudinal study." *Journal of Nutritional Science* 2020;9:e8. https://pubmed.ncbi.nlm.nih.gov/32166023/
2. Bezuglov E, Achkasov E, Vinogradov M, Baranova D, Shurygin V, Rudiakova E, Usmanova E, Vakhidov T, Malyakin G, Anishchenko I, Kapralova E. "Prevalence of Vitamin D Deficiency Among Young Elite Soccer Players Living Above 55 Degrees North Latitude and Evaluation of the Effectiveness of Self-Used Preventive Methods." *Translational Sports Medicine* 2025. https://pubmed.ncbi.nlm.nih.gov/40256208/
3. Bislev LS, Grove-Laugesen D, Rejnmark L. "Vitamin D and Muscle Health: A Systematic Review and Meta-analysis of Randomized Placebo-Controlled Trials." *J Bone Miner Res* 2021;36(9):1651-1660. https://pubmed.ncbi.nlm.nih.gov/34405916/
4. Sist M, Zou L, Galloway SDR, Rodriguez-Sanchez N. "Effects of vitamin D supplementation on maximal strength and power in athletes: a systematic review and meta-analysis of randomized controlled trials." *Frontiers in Nutrition* 2023;10:1163313. https://pubmed.ncbi.nlm.nih.gov/37661104/
5. Wacker M, Holick MF. "Sunlight and Vitamin D: A global perspective for health." *Dermato-Endocrinology* 2013;5(1):51-108. doi:10.4161/derm.24476. https://pubmed.ncbi.nlm.nih.gov/24494042/
6. Jung HC, Seo MW, Lee S, Kim SW, Song JK. "Vitamin D3 Supplementation Reduces the Symptoms of Upper Respiratory Tract Infection during Winter Training in Vitamin D-Insufficient Taekwondo Athletes: A Randomized Controlled Trial." *International Journal of Environmental Research and Public Health* 2018;15(9):2003. https://pmc.ncbi.nlm.nih.gov/articles/PMC6164435/
7. Ip TST, Fu SC, Ong MTY, Yung PSH. "Vitamin D deficiency in athletes: Laboratory, clinical and field integration." *Asia-Pacific Journal of Sports Medicine, Arthroscopy, Rehabilitation and Technology* 2022;29:22-29. https://pmc.ncbi.nlm.nih.gov/articles/PMC9256943/
8. Harju T, Gray B, Mavroedi A, Farooq A, Reilly JJ. "Prevalence and novel risk factors for vitamin D insufficiency in elite athletes: systematic review and meta-analysis." *European Journal of Nutrition* 2022;61(8):3857-3871. https://link.springer.com/article/10.1007/s00394-022-02967-z
9. Bordelon P, Ghetu MV, Langan RC. "Recognition and Management of Vitamin D Deficiency." *American Family Physician* 2009;80(8):841-846. https://pubmed.ncbi.nlm.nih.gov/19835345/
10. Office of Dietary Supplements, National Institutes of Health. "Vitamin D Fact Sheet for Consumers." https://ods.od.nih.gov/pdf/factsheets/VitaminD-Consumer.pdf
11. Larson-Meyer E. "The Importance of Vitamin D for Athletes." Gatorade Sports Science Institute. https://www.gssiweb.org/sports-science-exchange/article/sse-148-the-importance-of-vitamin-d-for-athletes
12. Webb AR, Kline L, Holick MF. "Influence of season and latitude on the cutaneous synthesis of vitamin D3: exposure to winter sunlight in Boston and Edmonton will not promote vitamin D3 synthesis in human skin." *Journal of Clinical Endocrinology and Metabolism* 1988;67(2):373-378. https://pubmed.ncbi.nlm.nih.gov/2839537/