She slept 8 hours but her body still crashed every afternoon: How low vitamin D became a trigger

When levels are suboptimal, the muscles feel perpetually weak

3 min readUpdated: Jan 30, 2026 07:52 AM IST

This deficiency profoundly impacts cellular energy production, as vitamin D is crucial for functioning of mitochondria, the powerhouse of cells.

Written by Dr Shovana Veshnavi

When 33-year-old Lara came to my OPD, she feared the worst. “I sleep a full eight hours, I go for a run in the evening after work, I eat clean but come afternoon, I feel sapped out, exhausted and feel sleepy. Some days I feel like crashing out despite cups of coffee. Nothing seems to be wrong, yet everything is. Am I seriously sick?” she asked me. This is a common question asked by many of my patients who are not aware of a key deficiency.

Such energy crashes happen when you have low vitamin D levels. Many do not realise that this micronutrient fuels up the body’s energy reserve. Her vitamin D levels were 12 ng/mL, far below the optimal range of 20-50 ng/mL.

The Vitamin D Crisis in India

Paradoxically, India — a sun-drenched nation — faces alarming vitamin D deficiency rates. Studies reveal that over 70% of urban Indians are deficient, largely due to indoor lifestyles, pollution blocking UV rays and cultural preferences for fair skin leading to sun avoidance. This deficiency profoundly impacts cellular energy production, as vitamin D is crucial for functioning of mitochondria, the powerhouse of cells.

Also read | Cardiologist clarifies if social media claim about vitamin D supplements harming heart and kidneys is true: ‘Should always be guided by a blood test’

How deficiency triggers afternoon fatigue?

Vitamin D deficiency impairs the body’s ability to produce ATP, our cellular energy currency. When levels are suboptimal, the muscles feel perpetually weak. Vitamin D helps produce serotonin, a neurotransmitter that regulates mood and energy. A deficiency can cause lower energy levels and low mood. The afternoon crash occurs because cortisol — which naturally dips post-lunch — cannot adequately compensate when vitamin D levels are low, leaving you battling overwhelming lethargy. Low vitamin D can trigger inflammatory responses, leading to feelings of sleepiness.

The Circadian Connection

Your body’s natural circadian rhythm creates an afternoon dip between 2-4 pm. While this is physiologically normal, vitamin D deficiency exacerbates this decline. The vitamin helps regulate sleep-wake cycles and supports serotonin production, which converts to melatonin. When deficient, this delicate balance falters, intensifying fatigue regardless of the previous night’s sleep.

Also read | This is what happens to the body when your vitamin D stays below 12 ng/ml for six months

Beyond Sleep and Sunshine

Other contributing factors include heavy, carbohydrate-rich lunches typical in Indian cuisine, which spike blood sugar before crashing it dramatically. Dehydration in India’s climate, inadequate protein intake and sedentary office work compound the problem.

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Addressing afternoon fatigue requires a multifaceted approach: vitamin D supplementation under medical guidance, strategic meal timing with balanced macronutrients, brief post-lunch walks, and strategic sun exposure. Understanding that adequate sleep alone cannot overcome biochemical deficiencies is crucial for reclaiming your afternoon vitality.

As for Lara, her energy levels stabilised in two weeks after supplementation, her focus improved and she no longer reached out for a carbohydrate-heavy snack.

(The author is principal consultant, Internal Medicine, Max Super Speciality Hospital, Noida)