That heavy, hard-to-shake morning feeling that settles in around October? For a lot of us, the missing piece is a quiet little vitamin your skin makes from sunshine. Here is what is really going on, and how to give your body what it needs.
⏱️ 7-minute read · Words by Chiara Ugozzoli · Updated June 2026
TLDR: Vitamin D keeps your bones, muscles and immune system happy, and through the darker half of the year your skin makes very little of it. Health bodies suggest most adults aim for a daily top-up, and almost one in four people run low. A small daily supplement and a few smart food swaps usually sort it. For your own levels, a quick chat with your doctor or pharmacist is the surest route.
So what does vitamin D actually do for you?
Think of vitamin D as the backstage manager your body relies on every single day. It helps you absorb calcium, which keeps your bones and teeth strong, and it keeps your muscles working smoothly. According to the US National Institutes of Health Office of Dietary Supplements (ODS), your immune system also leans on vitamin D to fight off invading bacteria and viruses, and your nerves use it to carry messages between your brain and the rest of you.
When levels stay low for a long stretch, the UK National Health Service (NHS) explains that bones can soften, a condition called osteomalacia in adults, which shows up as aches and tenderness. So that vague, run-down, achy feeling many women describe through winter? Sometimes it traces back here. It is a gentle reminder that the tiredness you feel has a real, physical story behind it, and that story has a friendly fix.
Why do so many women come up short?
Here is the honest answer: geography and lifestyle. Your skin makes vitamin D from direct sunlight, and the NHS points out that from about late March to the end of September most people in the UK make all they need outdoors. Through October to early March, the sun sits too low for your skin to manage it. Glass blocks the process too, so a sunny desk by the window still leaves you short, as the ODS confirms your skin pauses production behind glass.
Some of us run low all year. If you have brown or Black skin, spend most days indoors, or usually keep your skin covered, the NHS suggests a daily supplement across all twelve months. Modern life nudges many women indoors for work, childcare and rest, so even in summer the sunshine route can fall short. And these gaps are common. The ODS reports that almost one in four people in the United States have vitamin D blood levels that are low or inadequate for bone and overall health. That is a striking share, and it explains why this nutrient comes up so often in conversation with friends and at the pharmacy counter.
Picture this. It is a grey Tuesday in November. You slept eight hours, yet you feel like you waded through treacle to reach lunchtime. Your shoulders ache, your mood dips, and you wonder what is wrong with you. For many women, the season itself is the clue, and a small daily habit can change how those months feel.
How much do you actually need?
The numbers are reassuringly simple. The NHS advises that adults need 10 micrograms (mcg) of vitamin D a day, and that everyone, including pregnant and breastfeeding women, should consider a daily supplement containing 10 mcg through autumn and winter. The ODS frames it slightly higher for daily intake from all sources, suggesting 15 mcg (600 international units, or IU) for adults aged 19 to 70, rising to 20 mcg (800 IU) once you pass 70.
Those figures sit close together once you know the conversion: the NHS explains that 1 microgram of vitamin D equals 40 IU, so 10 mcg is the same as 400 IU. A standard high-street supplement of 10 to 25 mcg fits comfortably inside both sets of guidance for most women. The takeaway is calm and clear: you can pick up a sensible dose on a normal shopping trip, and it will do its quiet work day after day.
Can you get enough from food alone?
Food helps, and it is a lovely place to start, though the NHS is candid that few foods carry much vitamin D, which is why a supplement does the heavy lifting in winter. The richest natural sources are oily fish such as salmon, sardines, trout, herring and mackerel. After that come egg yolks, red meat, and fortified foods like some breakfast cereals and fat spreads. The ODS adds that mushrooms offer a little, and some are grown under ultraviolet light to lift their content.
A simple, cosy way to raise your intake: build one or two oily-fish meals into your week. A warm salmon traybake on a Sunday, sardines on sourdough for a quick lunch, a soft-boiled egg with your morning toast. These small rituals add up, and they feel like a small act of self-care. Pair them with a daily supplement through the dark months and you have covered most of the ground with very little fuss.
Try this tonight: Pop a 10 mcg vitamin D supplement next to your kettle or your toothbrush, somewhere you already go every evening. Vitamin D is fat-soluble, so the ODS suggests taking it with a meal or snack that includes a little fat, which helps your body absorb it. Make it part of your wind-down, and future-you will feel the difference by spring.
Could you take too much?
Yes, and this is the one place to stay mindful, because vitamin D is stored in the body. The NHS advises adults to stay below 100 micrograms (4,000 IU) a day, since taking very large amounts over a long period lets too much calcium build up, which can weaken bones and strain the kidneys and heart. The good news: you would struggle to reach that with a sensible high-street supplement, and the NHS confirms you can stay safe in the sun, because your skin self-limits and makes only what it needs.
If a doctor has prescribed a different dose for you, follow their advice. And if you take medicines such as statins, steroids or certain water tablets, the ODS notes vitamin D can interact with them, so a quick word with your pharmacist keeps things safe and simple. This is the kind of small check-in that takes two minutes and buys real peace of mind.
Should you get a blood test?
If you feel persistently tired, achy or low through the colder months, a vitamin D blood test offers real clarity. The ODS explains that levels of 50 nanomoles per litre (nmol/L), which equals 20 nanograms per millilitre, are adequate for most people, while readings under 30 nmol/L are too low for healthy bones. Your doctor can arrange a test and read it alongside everything else going on with you, which beats guessing.
Many women find that naming the issue is half the relief. Once you know where you stand, a daily habit and a couple of food swaps turn an invisible drain into something you actively manage. That sense of being back in charge feels wonderful, and it tends to ripple outward into how you sleep, move and feel about the season as a whole.
The gentle takeaway
Vitamin D is one of the kindest, lowest-effort wins in your wellbeing toolkit. Through autumn and winter, a small daily supplement of around 10 mcg keeps most women topped up, a few oily-fish meals add a natural boost, and a quick blood test clears up any lingering questions. Keep your intake within the safe ceiling, lean on sunshine in the warmer months, and let the habit run quietly in the background. Your bones, your muscles and your mood will thank you, season after season.
PrettyWell is a women’s lifestyle and wellbeing magazine. This article shares general information and wellbeing perspectives to help you ask better questions and feel more in charge; for anything about your own health, please speak with a qualified healthcare professional.
References
- National Health Service (NHS), “Vitamin D.” https://www.nhs.uk/conditions/vitamins-and-minerals/vitamin-d/
- US National Institutes of Health, Office of Dietary Supplements (ODS), “Vitamin D: Fact Sheet for Consumers.” https://ods.od.nih.gov/factsheets/VitaminD-Consumer/
