Every year when winter creeps in, so does the sudden dip in everyone’s mood, energy, immunity — and yes, vitamin D. It’s one of those nutrients your body heavily relies on sunlight for, so the moment the days get shorter, the skies stay gloomy, and we wrap ourselves in layers, the natural production just… collapses. It’s not dramatic — it’s simply how the body works.
To understand this winter drop and what you can realistically do about it, we checked in with Dietitian Fareeha Jay, whose insights line up with the growing research around seasonal vitamin D deficiency.
Why Vitamin D Crashes in the Colder Months
During summer, sunlight is strong enough for your skin to produce vitamin D even in short bursts outdoors. But from late October onwards, the sun sits too low in the sky — the UVB rays just aren’t strong enough. So even if you spend hours outside, your skin isn’t making the vitamin D you need.
Fareeha points out that “winter deficiency is incredibly common,” because most people assume diet alone will cover the gap — but foods naturally high in vitamin D are extremely limited, and not nearly enough to maintain healthy levels.
How Vitamin D Works in the Body — In the Simplest Terms
Vitamin D behaves more like a hormone than a typical vitamin. Once sunlight hits the skin and triggers its production, the body converts it into an active form that supports:
- calcium absorption
- bone and teeth strength
- muscle function
- immune regulation
So when vitamin D dips, these systems take the hit. That’s why winter often brings a mix of fatigue, body aches, lower immunity, and that general “winter slump” we all know too well.
Signs You Might Be Low on Vitamin D
The symptoms aren’t always loud — in fact, they’re usually subtle enough to ignore:
- persistent tiredness
- muscle weakness or cramps
- bone or lower-back aches
- more frequent infections
- mood dips or feeling “sluggish”
- in kids: irritability or slow growth
Most people realize something’s wrong only once it becomes severe enough to disrupt daily life.
Fareeha Jay’s Recommendations for Winter
Based on her clinical experience and current research, Fareeha emphasises three things:
1. Take a daily 10 mcg supplement throughout autumn and winter
Not a weekly mega-dose — your body absorbs smaller daily amounts more efficiently.
2. Always take it with food that contains some healthy fat
Vitamin D is fat-soluble, so having it with eggs, yogurt, avocado, nuts or oily fish helps it absorb better.
3. Use food as support, not the main source
Oily fish, egg yolks, fortified cereals and fortified milk alternatives help maintain your levels — but supplements are still essential in winter.
She adds that people with darker skin, those who stay indoors most of the day, kids under five, older adults, and individuals who cover most of their skin are at a higher risk of deficiency and should stay especially consistent with their supplements.
A daily supplement, some sunlight when you can get it, and a diet that includes vitamin-D-rich foods — that’s your winter formula. The colder months already slow the body down, so keeping your vitamin D steady can make a noticeable difference in energy, immunity, and overall wellbeing.
Disclaimer:
This article is based on insights from Dietitian Fareeha Jay and current research. It’s meant to give you a clear, helpful heads-up — not replace medical guidance. If you have symptoms, existing health conditions, or are unsure about supplements or dosage, it’s always best to consult your doctor or a qualified healthcare professional.
About Fareeha Jay Anwar
Fareeha Jay is a Registered Dietitian specializing in South Asian nutrition. With a background in anthropology and dietetics, she combines cultural understanding with nutritional science to provide personalized dietary guidance.
Sources: NHS, NIH, Public Health Agency
