If you know or suspect your vitamin D is low, the fix is usually straightforward — but "just take a supplement" glosses over a few decisions that actually matter: which form, how much, when to take it, and how to know it's working. Here's how to approach it properly.
Vitamin D is a fat-soluble vitamin, often called the "sunshine vitamin" as it's the only nutrient the body makes from direct sunlight on the skin. Vitamin D from sun, food, or supplements all need to be converted in the liver to 25-hydroxyvitamin D, then further converted in the kidneys to its active form, calcitriol. It's essential for calcium and phosphorus absorption, bone health, and neuromuscular and immune function.
Which form of vitamin D should you take?
Supplements are generally available as D2 (ergocalciferol) or D3 (cholecalciferol). D3 is the form your body makes naturally from sunlight and is generally considered more effective at raising and maintaining blood levels, so it's the better default choice unless you're vegan, in which case D2 (or a lichen-derived vegan D3) is the practical option. Capsules, tablets, and sprays are all effective — the best format is whichever one you'll actually take consistently.
How much vitamin D should you take?
The Scientific Advisory Committee on Nutrition (SACN) recommends a daily supplement of 10 micrograms (400 IU) for everyone in the UK aged 5 and over, particularly from October to March when sunlight exposure is limited. If you've been told you have a confirmed deficiency, your GP or nutritionist may recommend a higher, supervised dose for a set period before dropping back to a maintenance amount — higher doses shouldn't be taken long-term without guidance.
What are the best dietary sources, if you want to top up through food?
Dietary sources are limited compared to other vitamins, but can help alongside a supplement:
- Cod liver oil
- Salmon and rainbow trout
- Sardines (canned in oil)
- Mushrooms (light-exposed)
- Eggs
- Tuna and beef liver
- Fortified milk, plant milks, and cereals
- Cheddar cheese
If you're vegetarian or vegan, dietary options are more limited still — see our guide to the best vitamin D foods for vegans for more detail.
How to improve absorption
Vitamin D is fat-soluble, so it's absorbed better when taken with a meal containing some fat, rather than on an empty stomach. Consistency matters more than exact timing — taking it at the same time each day, alongside a meal, is the simplest way to build a habit that actually sticks.
How do you know if it's working?
The only reliable way to track your progress is a follow-up blood test, typically recommended around 3 months after starting or adjusting a supplement. Symptoms alone aren't a reliable guide, since many people with low vitamin D don't have noticeable symptoms in the first place, and improvements can be gradual.
FAQ
How long does it take for a vitamin D supplement to work?
Blood levels typically start improving within a few weeks, but most guidance recommends retesting around 3 months after starting a new dose to properly assess the change.
Is it better to take vitamin D daily or weekly?
Daily dosing at a standard maintenance level is the most common approach and is easiest to build into a routine. Higher, less frequent doses are sometimes used under medical supervision for confirmed deficiencies, but this should be guided by a professional rather than self-directed.
Can you take vitamin D with other supplements?
Vitamin D is often paired with calcium or magnesium, as they work together in bone health. If you're taking multiple supplements, it's worth checking for overlapping doses rather than assuming they simply add up safely.
If you're not sure whether your current approach is actually working, our at-home Vitamin D test can confirm your levels without waiting for a GP appointment.
