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As winter season arrives with shorter days and everyone's lifestyle changes, common vitamin deficiencies become a major problem. Reduction of sunlight exposure, alter and unhealthy diets, and less outdoor activity can worsen or cause critical nutrient deficiencies.
This article focuses on four winter deficiencies: Vitamin D, Vitamin B12, Iron, and Folate. It will cover their seasonal susceptibility, health problems, and strategies for test, diagnosis, prevention, and management during winter months.
Symptoms of vitamin deficiencies often worsen in winter.
Diagnosing these deficiencies involves assessing symptoms, risk factors, and laboratory analyses.
Vitamin d deficiency diagnose from blood test measuring serum 25-hydroxyvitamin D (25(OH)D).
Deficiency is generally <25-30 nmol/L (<10-12 ng/mL); insufficiency is 20-30 ng/mL (50-75 nmol/L); optimal levels are ≥50 nmol/L (≥20 ng/mL), with some aiming for 75-100 nmol/L (30-40 ng/mL). Screening is advised for at-risk groups.
Involves clinical assessment, risk factor evaluation, and blood tests.
Initial tests include Complete Blood Count (CBC) for megaloblastic anemia and serum vitamin B12 (cobalamin). If levels are indeterminate (200–300 pg/mL or 148–221 pmol/L), more sensitive markers like methylmalonic acid (MMA) and homocysteine (elevated in deficiency) or holotranscobalamin (holoTC) are use. Tests for anti-intrinsic factor antibodies or serum gastrin may be done for suspect pernicious anemia. Definitive deficiency is typically <150 pg/mL (111 pmol/L) or 200 ng/L.
Diagnose with blood tests for iron, hemoglobin (Hb), ferritin, and transferrin saturation (TSAT).
Ferritin <30 μg/L indicates deficiency (without inflammation). TSAT <20% supports deficiency. CBC with indices (MCV, MCH, RDW) can show microcytic/hypochromic red cells; RDW >14.0% can suggest deficiency. A confirmatory rise in Hb of ≥10 g/L within two weeks of iron therapy indicates absolute iron deficiency. Screening is recommend for high-risk groups (infants, children, pregnant women, women of childbearing age).
Diagnose from clinical suspicion and lab tests.
Serum/plasma folate levels can fluctuate; Red Blood Cell (RBC) folate offers a more reliable long-term assessment. Elevated homocysteine can indicate folate deficiency (or B12 deficiency). Simultaneous testing for B12 deficiency is crucial, as folate supplementation can mask B12 hematological signs. MMA testing helps differentiate (elevated in B12 deficiency, not folate deficiency).
Addressing winter vitamin deficiencies requires dietary adjustments, supplementation, and medical intervention.
Supplementation for Vitamin D Deficiency
| Population Group | Age Range | Recommended Daily Vitamin D Intake | Notes / Duration |
| General Population | Adults & children >4 years | 10 mcg (400 IU) daily; 2,000 IU daily for adequate levels | Mainly recommended during autumn/winter |
| Infants | 0–1 year | ≥400 IU/day | Year-round supplementation |
| Children | 1–18 years | ≥600 IU/day; up to 1,000 IU/day | Higher doses may be require |
| Adults | 19–70 years | ≥600 IU/day; 1,500–2,000 IU/day may be needed | Base on deficiency risk |
| Older Adults | >70 years | ≥800 IU/day; 1,500–2,000 IU/day recommend | Supports bone and muscle health |
| High-Risk Individuals | All ages | ~4,000 IU/day; up to 10,000 IU/day under medical supervision | Includes obesity, malabsorption, dark skin, institutionalized; year-round |
Management of Vitamin D Deficiency:
| Category | Recommended Dose | Duration / Notes |
| Adults | 50,000 IU weekly or 6,000 IU daily | For 8 weeks; target vitamin D level >30 ng/mL |
| Adults (Severe Deficiency <12 ng/mL) | 50,000 IU weekly | Initial supplementation for 8 weeks |
| Children (1–18 years) | 2,000 IU daily or 50,000 IU weekly | For at least 6 weeks |
| High-Risk Adults | 10,000 IU daily | Initial correction phase |
| Maintenance – Adults | 1,500–2,000 IU daily | After achieving adequate levels |
| Maintenance – High-Risk Adults | 3,000–6,000 IU daily | Long-term maintenance |
| Maintenance – Children | 600–1,000 IU daily | Long-term maintenance |
Supplementation Vitamin B12 Deficiency:
Recommend for older individuals, vegans/vegetarians, and post-bariatric surgery patients. (Take medicine after advised by professional Doctor)
Management of Vitamin B12 Deficiency:
| Category | Recommended Dose | Duration / Notes |
| Adults | 50,000 IU weekly or 6,000 IU daily | For 8 weeks; target vitamin D level >30 ng/mL |
| Adults (Severe Deficiency <12 ng/mL) | 50,000 IU weekly | Initial supplementation for 8 weeks |
| Children (1–18 years) | 2,000 IU daily or 50,000 IU weekly | For at least 6 weeks |
| High-Risk Adults | 10,000 IU daily | Initial correction phase |
| Maintenance – Adults | 1,500–2,000 IU daily | After achieving adequate levels |
| Maintenance – High-Risk Adults | 3,000–6,000 IU daily | Long-term maintenance |
| Maintenance – Children | 600–1,000 IU daily | Long-term maintenance |
Iron Deficiency
Dietary Measures: Include lean meats, poultry, seafood. Plant sources: beans, lentils, dark leafy greens, fortified cereals, whole grains. Pair non-heme iron with Vitamin C-rich foods to boost absorption. Limit coffee, black tea, and calcium with iron-rich meals.
Supplementation Iron Deficiency
Pregnant women: 30 mg elemental iron/day. Infants (breastfed): 1 mg/kg/day from 4 months. Women of childbearing age/adolescent girls: daily oral iron for three months annually in high-prevalence areas. (Take medicine after advised by professional Doctor)
Pregnant women: 30 mg elemental iron/day. Infants (breastfed): 1 mg/kg/day from 4 months. Women of childbearing age/adolescent girls: daily oral iron for three months annually in high-prevalence areas. (Take medicine after advised by professional Doctor)
Management of Iron Deficiency Deficiency:
| Therapy Type | Indication | Dosage | Administration Guidelines | Duration | Common Side Effects |
| Oral Iron Therapy | First-line treatment for mild to moderate iron deficiency | Adults: 100–200 mg elemental iron dailyChildren: 3–6 mg/kg elemental iron/day (max 60 mg/day) | Take at least 30 minutes before meals; may be taken with a small amount of food if needed. Alternate-day dosing improves tolerability | Continue for 2–3 months after hemoglobin normalization to replenish iron stores | Gastrointestinal discomfort, nausea, constipation |
| Intravenous (IV) Iron Therapy | Intolerance to oral iron, malabsorption, significant blood loss, severe deficiency, or pregnancy with severe nausea/vomiting | Dose depends on iron deficit and formulation | Administered under medical supervision | As per clinical requirement | Injection-site reactions, rare allergic reactions |
Folate (Vitamin B9) Deficiency
Dietary Intake:
When winter's season and lifestyle shifts significantly impact nutritional values, exacerbating deficiencies in Vitamin D, B12, Iron, and Folate. Very less sunlight exposure contributes to vitamin D deficiency, which affects bone health, immunity, and mood.
Diet changes lead to potential shortfalls in B12 and Folate, critical for neurological function and energy. These factors, along with decreasing Vitamin D, can compromise iron, affecting oxygen circulation and warmth. Understanding winter's nutritional challenges empowers proactive measures: regular monitoring (especially for at-risk groups), dietary awareness, and medical supplementation are key to mitigating deficiency risks and safeguarding health throughout colder months.
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