Diet & Nutrition Fitness

Vitamin D Deficiency – How Affects Your Weight, Mood and Athletic Performance

Several weeks back I started feeling, well, a bit under the weather. Sidelined by an injury, I couldn’t run outdoors, which is something I usually do even in the dead of winter. Without the sun, and seemingly endless days of rain, I was running low on that all-important nutrient – Vitamin D.

Why Vitamin D Is So Critical

The “sunshine vitamin” as it’s often referred to, is actually a hormone vital to the maintenance of strong bones, muscle integrity, a healthy endocrine (hormone) system and proper immune function. Studies show low vitamin D levels are linked to autoimmune, cancer and cardiovascular diseases, as well as a higher risk for diabetes and multiple sclerosis. Depression and weight gain is also related and, often, overlooked symptom of vitamin D deficiency.

Vitamin D deficiency is a global health problem, affecting all ages and ethnicities. Statistics show over one billion people worldwide are vitamin D deficient. So, the chances you are, too.

Vitamin D is found in many foods, including wild-caught fish, eggs and fortified milk; however, it’s considered an unreliable source, in and of itself. Humans naturally produce vitamin D through sun exposure (UV rays), but due to inclement weather, being fully clothed and staying indoors, many of us become low or deficient at some point during the winter months.

Weight Gain, Hypothyroidism and Insulin Resistance

It’s an establish fact that vitamin D is directly linked to calcium absorption. What’s lesser known (and hotly debated) is the role calcium plays in terms of weight loss. One study, in particular, concluded that deficient vit D and calcium levels was significantly associated with the degree and severity of hypothyroidism. As most people know, unexplained weight gain is a hallmark feature hypothyroidism. Poor thyroid disfunction can also lower your basal metabolic rate, making losing weight (even with calorie restriction) difficult and frustrating.

Insulin resistance, a classic feature of Polycystic Ovarian Syndrome (PCOS) and a precursor to diabetes and other major health risks, is the body’s inability to effectively synthesis glucose at the cellular level. Insulin is a hormone produced in the pancreas that helps control glucose (blood sugar). Glucose is our body’s key source of energy, fueling our bodies to function. Research, although not conclusive, suggests healthy vitamin D levels improve insulin resistance and may actually protect against type 1 diabetes. Insulin resistance is linked to obesity, Dyslipidemia (an abnormal ratio of blood fats and cholesterol in the blood) and unhealthy visceral (abdominal) fat ratio.

The good news? Several recent studies demonstrate a correlation between higher vitamin D blood levels and leaner muscle mass (lower BMI).

The Winter Blues

There’s a growing body of evidence linking vitamin D deficiency to Seasonal Affective Disorder (SAD), depression and mood disorders. In several Scandinavian studies, researchers determined vitamin D played a significant role in a person’s sense of wellbeing, energy levels and overall happiness. Nordic countries, with their long, dark winters, are particularly at risk for vitamin D deficiencies and routinely counteract this with supplementation and light therapy.

Vitamin D supplements have also been found to enhance positive moods and reverse depressive symptoms. Healthy subjects were given various vitamin D IU during the winter. The results of that study concluded that vitamin D was able to significantly enhance a positive affect while reducing the negative affect.

It’s worth noting that most people tend to hunker down during winter, feeling less-inclined to be active and this may be in part due to their low levels of vitamin D. From personal experience, I can always tell when I’m getting a little low…I don’t “feel” as motivated (and, for me, that’s a HUGE red flag). I tested vitamin D deficient in the past and taking supplements significantly improved my overall mental and physical wellbeing.

Athletic Performance, Injury and Illness

Surprisingly enough, vitamin D deficiency is common among athletes. A review of several studies demonstrates a correlation between vitamin D sufficiency and optimal muscle function. Increasing levels of vitamin D helps reduce inflammation, pain and myopathy (muscle disease associated with cramps, stiffness and pain) while simultaneously increasing muscle protein synthesis, ATP (cell energy) concentration, strength, exercise capacity and overall physical performance.

One UK study, which tested athletes from three diverse sports, concluded that vitamin D supplementation significantly improved sprint times and vertical jump ability, whereas the placebo group showed no performance improvement. Another study involving professional soccer players showed a direct link between improved muscular strength, speed and VO2max (aerobic capacity) with adequate vitamin D levels. More recently, new evidence presented in International Journal of Sports Nutrition and Exercise Metabolism, demonstrated low vitamin D levels in collegiate athletes compromised their muscular strength and power. This research, which tested male and female athletes from a different seasonal sports, determined adequate levels of vitamin D were essential to optimal athletic performance.

Conclusion Thoughts, Dosage Suggestions and Links

The important role of vitamin D in our overall mental and physical wellbeing cannot be underestimated. As an athlete, I’m also keenly aware of how important vitamin D is in terms of athletic performance, as well as a positive mindset.

After supplementing my diet with Vitamin D3 5,000 IU per day, I immediately started feeling better. The biggest change was in my mood and energy. I still tested a subclinical thyroid, but I’m not feeling that overwhelming sense of fatigue and listlessness. Mentally, I noted a significant uptick in my cognitive function…BONUS!

As alway, when considering adding any significant dietary change involving supplements you’re not familiar with, I recommend consulting your doctor or a naturopath to determine your current blood levels and a sufficient (and safe dosage). The Mayo Clinic offers in-depth guidelines for supplementing vitamin D to treat various health concerns, including heart disease, viral infection, fractures and, of course, deficiency.

In any sense, bear in mind vitamin D levels must be check-and-adjusted with the seasons, your particular medical/health needs and taken within safe levels to avoid toxicity. And, if you’re dealing with a more serious health concern, especially depression, please seek proper medical attention as soon as possible.


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DR J 2211 – Rachael Jezierski, PhD