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Ask five people how to get more vitamin D and you’ll get five answers: a supplement bottle, a fillet of salmon, twenty minutes in the garden, a fortnight in Spain, or a blood test and a prescription. They’re all legitimate routes. None of them works well for everybody.
That’s the part most articles skip. Vitamin D matters for bone density, muscle function, calcium absorption and immune signalling, and low levels are genuinely common in anyone living north of roughly 37° latitude, working indoors, or carrying more melanin in their skin. But the ways of fixing it differ enormously in cost, reliability and risk. Here’s how they stack up.
What you’re actually trying to achieve
Before comparing sources, it helps to know what the nutrient is doing. Past the well-known bone connection, vitamin D receptors sit in muscle tissue, immune cells and the gut lining, which is why low levels show up as fatigue, frequent infections and aching joints as often as they do as brittle bones. What vitamin D actually does in your body is worth five minutes if you want the biology. The key detail for this comparison is that the effect is dose-dependent: dragging levels from deficient to sufficient does far more than topping up from sufficient to optimal.
Sunlight: efficient, free, and wildly inconsistent
Your skin makes vitamin D when UVB rays convert 7-dehydrocholesterol in the epidermis into cholecalciferol, the same form found in animal-source supplements. It’s the only route that can produce serious quantities quickly. A fair-skinned adult in shorts and a t-shirt at midday in July can generate somewhere between 1,000 and 10,000 IU in 15 to 30 minutes, and the body self-regulates by degrading the surplus.
What it gives you:
- Zero cost, zero packaging, no dosing decisions.
- You produce your own D3, the form your body uses most readily.
- Short exposures also support nitric oxide release, which affects blood pressure independently of vitamin D.
Where it falls apart is everything else. From roughly October to March, anyone above 37° latitude (everything north of San Francisco, Athens or Seoul) sees the UV index sit below 3, the threshold for meaningful skin synthesis. Sunscreen at SPF 30 cuts production by around 95%. Glass blocks UVB entirely, so the sunny window seat does nothing. Darker skin can need five to ten times longer in the sun for the same output. Ageing thins the skin’s supply of the precursor molecule, so a 70-year-old makes roughly a quarter of what a 20-year-old does from identical exposure. Stack skin cancer risk on top and deliberate sunbathing stops looking like a clean win.
Food: real vitamin D, but a lot of chewing
Food is the most appealing option on paper and the least practical in practice. A 100g fillet of wild salmon carries roughly 570 to 1,000 IU. Farmed salmon lands closer to 250 to 400 IU. A tin of tuna gives you about 150 IU, a single egg yolk around 40 IU, and a cup of fortified milk or plant milk somewhere between 100 and 120 IU. UV-exposed mushrooms can reach 400 IU per 100g, which is a neat trick if you like mushrooms.
Run the numbers and hitting 800 IU a day from food alone means oily fish most days of the week. That’s realistic for some households and a non-starter for vegetarians, anyone with a fish allergy, and anyone watching mercury intake. The compensations are genuine, though: oily fish brings omega-3 fatty acids, protein and selenium along with the vitamin D, and getting omega-3 into your actual week delivers benefits no capsule of D3 will replicate.
Supplements: the option you can actually control
Supplements are boring, which is precisely their advantage. You know the dose, you can take them in February, and they don’t care what latitude you live at.
D3 versus D2
Two forms dominate the market. D3 (cholecalciferol) comes from lanolin in sheep’s wool, or from lichen for vegan versions, and is what your skin produces. D2 (ergocalciferol) is made from yeast. Head-to-head trials consistently show D3 raising blood levels higher and holding them there longer, though D2 still works and is often what you’re handed on prescription at 50,000 IU per week. If lanolin is a problem for you, lichen-derived D3 exists and performs like the animal version.
Format matters more than you’d think
Vitamin D is fat-soluble, so it needs dietary fat to be absorbed properly. Taken with a meal containing around 10 to 15g of fat, absorption can run 30 to 50% higher than on an empty stomach. That creates real practical differences between formats:
- Softgels suspended in oil are the most reliable low-effort choice.
- Liquid drops let you fine-tune the dose, useful for children or anyone on 400 IU rather than 2,000.
- Gummies are pleasant but frequently underdosed, and some carry a couple of grams of sugar per serving.
- Sprays work fine, though the evidence that sublingual absorption beats swallowing is thin.
How much, and how long
Official adult intake sits at 600 to 800 IU, with a tolerable upper limit of 4,000 IU daily. In practice, most people who test low need 1,000 to 2,000 IU to climb into the sufficient range, and it takes eight to twelve weeks to see the full shift. More is not automatically better: consistently clearing 4,000 IU without monitoring can push calcium too high, causing nausea, kidney stones and raised blood calcium over the long run.
Multivitamins and cod liver oil: the accidental sources
A lot of people get vitamin D without meaning to. A typical multivitamin carries 400 to 1,000 IU, which is a reasonable top-up but rarely enough on its own to correct a deficiency. It’s worth checking what a daily multivitamin can realistically do before buying one purely for its D content, since you’re paying for nine other ingredients you may not need. Cod liver oil is a different proposition: rich in vitamin D, but also in preformed vitamin A, which is toxic in large amounts. Stacking it with a separate D supplement is a bad idea, not a belt-and-braces one.
Testing: the only way to know any of this worked
You can cycle through sun, salmon and softgels for years without knowing whether your level actually moved. A 25-hydroxyvitamin D blood test costs relatively little in most countries and settles the question. Reference ranges vary by lab, but the usual reading is deficiency below 12 ng/mL, insufficiency between 12 and 20, and sufficiency from 20 upward, with a growing body of researchers arguing 30 to 50 is better for bone and immune outcomes. Test in late winter if you want to catch your annual low point, then retest about 12 weeks after changing anything.
If the idea of testing blind appeals about as much as guessing, a step-by-step plan for getting more vitamin D without guessing walks through the proper sequence: estimate, test, dose, retest, adjust.
Building the mix that fits your life
There’s no single best source, only the best combination for your circumstances. A few common patterns:
- Fair skin, outdoors often, low latitude. Sun covers most of it. Add 400 to 1,000 IU through winter and you’re finished.
- Office job, northern city, darker skin. Sun won’t reliably deliver. A daily 1,000 to 2,000 IU softgel or drop is the backbone, with food as a bonus rather than a plan.
- Over 65. Skin synthesis drops sharply and the kidneys convert vitamin D less efficiently. Supplement year-round and retest annually.
- Vegan. Fortified foods plus lichen-derived D3 or D2 cover it without animal inputs.
- Pregnant, or taking steroids, anticonvulsants or weight-loss medication. These all change how vitamin D is metabolised. Speak to a clinician before self-dosing.
The logic underneath every one of those is the same. Use sun when it’s available and reliable, use food for the co-nutrients that come with it, and use a supplement for consistency. Then check a blood level once, so you know which of the three you’re genuinely relying on rather than which one you assumed was covering you.
