Vitamin D Deficiency: The Silent Epidemic Crushing Your Energy Levels and Workout Recovery

Most athletes at one point or another hit a rough patch where performance falls short, even when they’re giving it everything they’ve got in the gym. However, many brush it off as just another bad workout.

Chronic fatigue and loss of drive could point to serious health concerns linked to nutrient deficiencies.

Instead of grinding harder, it’s smarter to pause and take a hard look at your nutrition.

As a personal trainer with over 17 years in the trenches, I’ve firsthand seen how vitamin D deficiency can wreck your energy and recovery. I’ve been there myself, and things got so severe it took medical intervention to bounce back.

In this article, I break down everything you need to know about vitamin D, including what it is, why you might be deficient, how to test your levels, and what you can do to boost your energy and dominate your workouts. I’ll also share my personal experience battling this issue.

What Is Vitamin D and Why Does It Matter?

Vitamin D is a hormone that powers energy, mood, and muscle recovery by boosting mitochondrial function, regulating serotonin, and supporting protein synthesis.

Protein synthesis is the process by which your body rebuilds muscle fiber after an intense training session, provided it has all the necessary nutrients and is allowed ample time to recover.

Research reveals that 50% of adults worldwide are vitamin D deficient. (1)

This shouldn’t come as a surprise, as most of us spend the majority of our days indoors, glued to our desks.

Even people who eat clean and train hard are vulnerable to vitamin D deficiency. Many people associate vitamin D deficiency symptoms, like sluggish performance, persistent fatigue, muscle soreness, and mood dips, with stress or overtraining, leaving the main issue undetected. (2)

Testing for Vitamin D Deficiency: Know Your Levels

Vitamin D levels are typically measured as 25-hydroxyvitamin D (25(OH)D) in the blood. Here’s how the ranges generally break down:

Status	Level (ng/mL)	Interpretation
Deficient	< 20 ng/mL	Too low; high risk of bone issues
Insufficient	20–29 ng/mL	Suboptimal; may affect muscle mass and immunity
Sufficient (Ideal)	30–50 ng/mL	Generally considered healthy
High	50–100 ng/mL	Still safe for many, monitor if using supplements
Potentially Toxic	> 100 ng/mL	Risk of toxicity

I must come clean. Recently, I was experiencing chronic fatigue, and it wouldn’t go away no matter what I did.

I took a few days off from training and increased my carbohydrate intake, thinking that my low-carb diet could be causing this issue. However, there was virtually no change in how I felt. My overall productivity plummeted, and my motivation hit rock bottom.

Then, I randomly came across an article that talked about the same symptoms I was feeling and linked them to vitamin D deficiency.

I got my blood work done right away, and the results completely shocked me. My vitamin D levels came back at a whopping 12 ng/mL. In fact, I got a call from the pathologist inquiring about my health.

This is when I knew things weren’t looking great.

As a writer and personal trainer, I spend most of my days indoors, and this resulted in an acute vitamin D deficiency since my direct sun exposure was close to zero.

You should aim for 30-50 ng/mL of vitamin D as it is the gold standard for energy, muscle repair, and health.

Accessing the 25(OH)D Test

While a vitamin D test might sound like a super niche thing, it is actually very common, and you can order this test through a lab like Quest or LabCorp. The best part? The 25(OH)D doesn’t break the bank.

Plus, you can take these tests in the comfort of your living room with at-home kits by pricking your finger and mailing a sample to the lab.

Most insurance plans cover doctor-ordered blood tests, and your healthcare provider will gladly write one up for you. Even though it is relatively inexpensive, check your policy to confirm you don’t have to pay for this test out of your pocket.

A vitamin D test will likely cost you less than your monthly fitness supplement bill.

Doctors usually recommend getting a vitamin D test every six to 12 months if you get limited sun exposure, have darker skin, or are experiencing persistent fatigue.

How Does Vitamin D Work

Now that you know the basics of vitamin D, let’s talk about why you feel drained when your D stores are inadequate.

Vitamin D supercharges mitochondria (the powerhouse of your cells). It optimizes ATP production, fueling every rep and physical activity. Without enough ATP, you fatigue faster and your endurance fades, negatively impacting your overall work capacity.

Vitamin D is one of the most important nutrients for bodybuilders, as it supports protein synthesis, lowers muscle inflammation, and slashes soreness. Maintaining optimal vitamin D levels can help you excel in the weight room and maximize muscle pumps and subsequent adaptations. (3)

It doesn’t end here; increasing your vitamin D intake can improve serotonin levels, the brain chemical responsible for keeping you upbeat and focused.

Experts believe that ample D intake can bolster your immune system and lower the risk of falling ill. It also enhances calcium absorption, strengthening your bones to handle heavier weights in the gym.

The Silent Epidemic: How Common Is Vitamin D Deficiency? 

After I was over the initial panic phase, and my doctor told me exactly what to do, I started researching how common vitamin D deficiencies actually were.

In the northern latitudes, like Canada and the UK, almost 60% of residents were vitamin D deficient because of the weaker sunlight. On the other hand, darker-skinned populations face higher risks, as melanin blocks UVB rays and hampers vitamin D synthesis.

Even in sunny regions like the Middle East, 50-80 percent of the population faces vitamin D deficiency, thanks to cultural practices limiting sun exposure. (1)

In my investigation, five factors stood out for increasing vitamin D deficiency:

• Limited sun exposure: Areas above 37 degrees latitude, working indoors, or using sunscreen curbs UVB absorption.
• Poor diet: Eating a restrictive diet like the vegan diet increases the odds of a vitamin D shortfall. Opt for foods like fatty fish or fortified dairy to fix this.
• Skin pigmentation: Darker-skinned individuals need three to five times more sun exposure to produce the same vitamin D as their lighter-skinned counterparts.
• Age: Younger people synthesize more vitamin D than those over 65.
• Obesity: Excess visceral fat traps vitamin D, reducing its bioavailability. A BMI over 30 doubles your risk of D deficiency.

Many of my clients previously blamed their persistent fatigue on a tough deadlift session or a bad night’s sleep. However, things cleared up after they took the 25(OH)D test.

Vitamin D Deficiency Checklist

Answer these five simple questions to assess if you are dealing with a vitamin D deficit:

• Do you feel drained despite sleeping for eight hours each night?
• Are your gym lifts taking a hit?
• Does your muscle soreness drag on for multiple days after each workout?
• Do you fall sick often?
• Are you more irritable than usual and have lost the motivation to train?

If you nod to two or more of these questions, there is a high probability that you have low vitamin D levels.

At this point, you should get a blood test done and take appropriate steps to plug the gaps in your nutrition.

Solutions: Boosting Your Vitamin D Levels Naturally and Safely

You can boost your vitamin D levels in different ways:

Safe Sun Exposure

Sunlight is undoubtedly the best source of vitamin D, and your skin synthesizes it optimally.

You should aim for 10-30 minutes of midday sun (11 a.m. to 3 p.m.) on bare skin, like arms, legs, or back, at least two to three times a week. Research shows that this produces 10,000-20,000 IU of vitamin D naturally. (4)

Dietary Sources

Although food alone can’t help you achieve optimal vitamin D levels, it can play a crucial role when combined with other strategies.

Fatty fish like salmon, egg yolks, milk, and yogurt are good sources of vitamin D, and should be staples in your diet.

Vegetarians and vegans should be extra careful. Add mushrooms and fortified plant milks to the diet to negate the risk of D deficiency. Experts recommend pairing these with healthy fat sources like avocados to improve vitamin D absorption.

Supplementation

The Endocrine Society recommends taking a 1,000-4,000 IU vitamin D3 supplement daily. You can find them in pill, capsule, drops, or gummy form.

In my case, my doctor prescribed a 60,000 IU vitamin D3 shot that I had to take once a week.

Weekly and daily vitamin D supplements essentially work the same way. You should always follow your doctor’s recommendations when it comes to vitamin D dosages. Over-supplementation can harm your kidneys, whereas under-dosing can render the prescription useless.

Conclusion

Low vitamin D levels are the new age epidemic that no one is talking about. It can hamper your energy levels, physical and mental performance, and increase the risk of fractures in extreme cases.

Once you find out your vitamin D levels are low, start by spending more time in the sun. Next, adjust your diet and bring in supplements to cover the shortfall. Stay consistent and you’ll see the desired results within 12 weeks. Best of luck!

References:

1. Cui A, Zhang T, Xiao P, Fan Z, Wang H, Zhuang Y. Global and regional prevalence of vitamin D deficiency in population-based studies from 2000 to 2022: A pooled analysis of 7.9 million participants. Front Nutr. 2023 Mar 17;10:1070808. doi: 10.3389/fnut.2023.1070808. PMID: 37006940; PMCID: PMC10064807.
2. Aspell N, Laird E, Healy M, Lawlor B, O’Sullivan M. Vitamin D Deficiency Is Associated With Impaired Muscle Strength And Physical Performance In Community-Dwelling Older Adults: Findings From The English Longitudinal Study Of Ageing. Clin Interv Aging. 2019 Oct 15;14:1751-1761. doi: 10.2147/CIA.S222143. PMID: 31686797; PMCID: PMC6800555.
3. Hirono T, Ikezoe T, Taniguchi M, Tanaka H, Saeki J, Yagi M, Umehara J, Ichihashi N. Relationship Between Muscle Swelling and Hypertrophy Induced by Resistance Training. J Strength Cond Res. 2022 Feb 1;36(2):359-364. doi: 10.1519/JSC.0000000000003478. PMID: 31904714.
4. Office of Dietary Supplements. Vitamin D: Fact Sheet for Health Professionals. National Institutes of Health. Updated August 2023. Accessed May 16, 2025. https://ods.od.nih.gov/factsheets/VitaminD-HealthProfessional/

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