Winter can feel like a natural time to slow down, but when profound fatigue, bone pain, and persistent low mood set in, it might be more than just the winter blues. This complex set of symptoms is often dismissed, yet experts warn they could be subtle indicators of one of the most widespread nutritional deficiencies: Vitamin D deficiency.
As sunlight exposure dwindles in the colder months, the body`s primary way of producing this essential nutrient is impaired, leading to consequences that affect everything from energy levels and immune function to bone health.
This winter, medical experts guide you through the latest diagnostic standards, the non-deficiency causes of fatigue, and the practical steps you can take to maximise your health and vitality throughout the winter and into the new year.
Standard blood tests to screen for physiological causes of fatigue
When a patient presents with persistent fatigue, clinicians typically begin with a broad set of basic blood tests to identify the most common physiological contributors. According to Dr Geetanjali Patil, consultant pulmonologist at Ruby Hall Clinic Wanowire, these include:
1. Complete Blood Count (CBC) to rule out anaemia or infection.
2. Thyroid Function Tests (TSH, Free T4) to assess for hypothyroidism.
3. Vitamin D (25-OH Vitamin D) to detect deficiency that often worsens in winter.
4. Vitamin B12 levels are checked to identify deficiencies linked to low energy, neuropathy, or cognitive slowing.
5. Iron studies, including serum ferritin, serum iron, Total Iron Binding Capacity (TIBC), and transferrin saturation, help diagnose iron-deficiency anaemia or low iron stores even before anaemia is visible on CBC.
6. Many clinicians also add fasting blood glucose, HbA1c, and basic metabolic panel to rule out diabetes, electrolyte imbalances, kidney dysfunction, or dehydration, all of which can contribute to fatigue.
Differential diagnosis when blood tests are normal
If initial blood work appears normal, non-deficiency causes of fatigue become important considerations. “Seasonal Affective Disorder (SAD) is particularly relevant in winter and is linked to reduced sunlight exposure, disrupted circadian rhythm, low serotonin activity, and excessive melatonin production,” notes Dr Geetanjali.
She lists other possible causes:
1. Chronic stress and burnout, which can manifest as profound physical fatigue because prolonged cortisol dysregulation affects sleep, immunity, and energy levels.
2. Sleep-related issues, particularly insomnia, poor sleep hygiene, and circadian rhythm disorders.
3. Depression, generalized anxiety, post-viral fatigue, perimenopause/menopause in women, chronic pain conditions, restless legs syndrome, medication side effects, and chronic fatigue syndrome, especially if symptoms are prolonged and unexplained.
Musculoskeletal pain with fatigue: Conditions to rule out
Non-injury bone or joint pain paired with fatigue often points toward systemic medical conditions. Dr Geetanjali highlights that one of the first considerations is Vitamin D deficiency, as low Vitamin D commonly causes diffuse bone aches, muscle weakness, and fatigue.
Conditions to rule out include:
1. Autoimmune or inflammatory conditions such as rheumatoid arthritis, lupus, fibromyalgia, or polymyalgia rheumatica.
2. Thyroid dysfunction, particularly hypothyroidism, which can cause generalized muscle aches and joint stiffness.
3. Osteomalacia (softening of bones due to long-standing Vitamin D deficiency) and early osteoporosis.
4. Chronic infections (such as EBV, TB, or Lyme in endemic regions), metabolic issues like hyperparathyroidism, and rare haematological disorders such as multiple myeloma may be considered if symptoms persist or are accompanied by red flags such as night sweats or unexplained weight loss.
Role of undiagnosed sleep issues
Sleep disorders are one of the most overlooked contributors to chronic fatigue. Dr Patil explains, “Obstructive sleep apnoea (OSA) is especially common and can occur even in people who are not overweight. It leads to repeated nighttime breathing interruptions, poor oxygenation, and non-restorative sleep, often leaving patients exhausted despite seemingly sleeping for 7 to 8 hours.”
A formal sleep study (polysomnography) is typically recommended when a patient experiences symptoms such as:
1. Loud snoring, witnessed apnoea’s, choking episodes at night.
2. Morning headaches or excessive daytime sleepiness.
3. Unexplained fatigue that persists despite normal labs.
4. Resistant hypertension.
Expected timeline for improvement in deficiency symptoms
Recovery from Vitamin D deficiency is gradual because the body has to rebuild the Vitamin D gap. Dr Bhaskar S, general physician and internal medicine specialist at Apollo One, Bengaluru outlines the different expected recovery timelines:
1. Many patients notice mood changes, increased awareness, and energy enhancement after 2 to 4 weeks of Vitamin D supplementation.
2. Bone pain, muscle weakness, or muscle achiness usually take 6 to 12 weeks to show signs of improvement.
3. Complete resolution of severe deficiencies may take anywhere from 3 to 6 months to fully correct.
4. Periodic serum 25(OH)D monitoring is vital for insuring safe and effective results.
Dr Mahesh D M, consultant, endocrinology at Aster CMI Hospital, Bengaluru adds, “Patients with chronic kidney disease, malabsorption disorders, post-bariatric surgery recovery, liver disease, or inflammatory bowel disease may need increased or specially formulated doses due to the lower absorption capacity.”
Most effective dietary sources and essential micronutrients
Bhaskar believes that Vitamin D needs to come from diet and supplements during winter months when low amounts of UVB light are available. He shares Vitamin D sources:
1. Vitamin D3 (cholecalciferol), which is produced from animal sources (like salmon, eggs, etc.) and fortified foods (like soy milk and cereals).
2. Some mushrooms contain UV (ultraviolet) light which creates Vitamin D2.
Mahesh and Bhaskar both stress that other micronutrients work together with vitamin D to provide synergy:
1. Magnesium: Promotes vitamin D activation. Food sources include nuts, seeds, leafy greens.
2. Vitamin K2: Responsible for directing calcium to the bones. Good food sources include beef, eggs, cheese, and spinach.
3. Calcium: Strengthens bones when used in conjunction with vitamin D.
4. Zinc: Helps convert vitamin D and supports the immune system.
These nutrients are essential for optimizing absorption and positively impacting both skeletal health and extra-skeletal health.
Evidence-based lifestyle changes to boost energy
Dr Bhaskar and Dr Mahesh share realistic, healthy lifestyle changes to reduce tiredness and to naturally increase Vitamin D levels:
1. Spend time in sun: Expose yourself to sunlight for at least 15 to 20 minutes per day. The time you need will vary by season and skin type.
2. Consume foods and fluids that are high in vitamin D: Follow a healthy eating pattern that includes Vitamin D foods, magnesium, and K2, and consume adequate fluids (2 to 3 litres of water daily) to ensure that the body has maximum absorption of Vitamin D.
3. Be active: Engage in a moderate level of physical activity (walking, yoga, swimming), this will have a positive effect on increasing your stamina and decreasing muscle strain. Set a timer to remind you to stretch or take a deep breath every 20 minutes of time you are working that day.
4. Sleep and balance energy levels: Develop good sleep habits, also called sleep hygiene. Caffeine consumption and/or alcohol consumption in the evening should be limited to help keep your energy levels balanced and stable.
5. Schedule your meals: Keep your meals on a consistent schedule throughout the day. Do not eat heavy meals at night.
Dr Mahesh states that small changes to your daily routine are better than trying to find a quick solution to restore your daily vitality.
Medications and supplements that may worsen fatigue
Certain everyday medications can actually slow down the central nervous system or disturb metabolic pathways, ultimately leading to fatigue. Dr Bhaskar lists the following potential culprits:
1. Common antihistamines like diphenhydramine and cetirizine often cause sedation and lethargy.
2. Certain antidepressants can create a sedating effect which contributes to slight dizziness.
3. Rarely, statins used to manage cholesterol may cause muscle pain and lead to tiredness.
4. Over usage of sedatives (such as benzodiazepines) and sleep aids like melatonin can also lead to weakness or an uneasy feeling the next morning.
5. Unwanted doses of supplements such as iron and even Vitamin D may lead to tenderness and pain in the body.
Dr Mahesh adds that fatigue can also be caused by:
1. High dose or unwanted medications like heart medications, anxiety drugs, muscle relaxants, and certain diabetes medicines that disturb blood sugar flows.
2. Supplements like magnesium, valerian root, and herbal sleep formulas can also disturb sleep formations and cause drowsiness.
He concludes, “If fatigue persists, a person should consult an expert or doctor to evaluate their medication list, as unexplained laziness or tiredness is often linked to drug usage or inappropriate dosing.”
