Vitamin D Supplements Compared: Dose, Form & What the NHS Won't Tell You

Quick Verdict

The NHS recommends 400 IU (10mcg) of vitamin D daily. This is the minimum to prevent deficiency, not the amount needed for optimal health, bone density, immune function, or athletic performance. Research consistently uses 1000-4000 IU. Most people in the UK — especially those who train indoors, work desk jobs, or have darker skin — should be supplementing at 1000-2000 IU minimum, with 3000-4000 IU through the winter months.

Product Overview

Factor	Boots Own-Brand	H&B Vitamin D	BetterYou Spray	Solgar D3	Myprotein D3
Dose per serving	400 IU (10mcg)	1000 IU (25mcg)	3000 IU (75mcg)	4000 IU (100mcg)	2500 IU (62.5mcg)
Form	D3 (cholecalciferol)	D3 (cholecalciferol)	D3 (cholecalciferol)	D3 (cholecalciferol)	D3 (cholecalciferol)
Delivery	Tablet	Tablet	Oral spray	Softgel	Softgel
Supply	90 tablets	90 tablets	~100 sprays	100 softgels	180 softgels
Price	~£3.50	~£6.00	~£9.00	~£12.00	~£8.00

Cost Comparison (Normalised to Daily Use)

Brand	Dose (IU)	Days supply	Price per day	Price per 1000 IU
Boots Own-Brand	400	90 days	£0.04	£0.10
H&B Vitamin D	1000	90 days	£0.07	£0.07
Myprotein D3	2500	180 days	£0.04	£0.02
BetterYou Spray	3000	~100 days	£0.09	£0.03
Solgar D3	4000	100 days	£0.12	£0.03

Myprotein offers the best value per 1000 IU at roughly 2p. But the more important question is which dose you need.

The NHS 400 IU Problem

The NHS 400 IU recommendation is based on preventing rickets and severe deficiency in the general population. It is not an optimal target for:

Active individuals who need vitamin D for muscle function and recovery
People who work indoors and get minimal sun exposure
Anyone living above the 37th parallel (the entire UK qualifies — your skin cannot produce vitamin D from sunlight between October and March)
People with darker skin who require 3-5x more sun exposure to produce the same amount

Blood levels of 25-hydroxyvitamin D below 25 nmol/L indicate deficiency. The NHS targets 25+ nmol/L. Sports medicine research suggests 75-125 nmol/L is optimal for performance, immune function, and bone health. Getting from 25 to 75+ nmol/L typically requires 1000-4000 IU daily, depending on your starting level, body weight, and sun exposure.

D3 vs D2: This Matters

Vitamin D3 (cholecalciferol) — derived from animal sources (lanolin from sheep’s wool, or lichen for vegan versions). More effective at raising and maintaining blood levels. All five products here use D3.

Vitamin D2 (ergocalciferol) — derived from fungi. Less effective at raising blood levels, shorter half-life, requires higher doses. Historically prescribed by the NHS because it is cheaper. Avoid if you have a choice.

If you see a supplement labelled simply “Vitamin D” without specifying D3, check the ingredients. It may be D2.

Delivery Method: Spray vs Tablet vs Softgel

Oral spray (BetterYou) — absorbs through the buccal membrane in the mouth, bypassing the gut. Some evidence suggests slightly faster absorption. Useful for people with digestive issues or fat malabsorption. Convenient but more expensive per IU.

Softgel in oil (Solgar, Myprotein) — vitamin D is fat-soluble and absorbs best with dietary fat. Softgels suspended in oil (often olive or coconut) provide the fat needed for absorption in one package. This is the most reliable delivery method.

Dry tablet (Boots, H&B) — requires you to take it with a fat-containing meal for proper absorption. If you take it with your morning coffee on an empty stomach, you are absorbing significantly less. Most people do exactly this.

The Fat-Soluble Factor

Vitamin D is fat-soluble, meaning:

Take it with food containing fat — eggs, avocado, nuts, butter, olive oil
It accumulates in the body — unlike water-soluble vitamins, you can technically take too much over long periods
The upper tolerable limit is 4000 IU/day according to most guidelines, though toxicity is extremely rare below 10,000 IU/day
Getting a blood test is the only way to know your actual level and dial in the right dose

If in doubt, 2000 IU daily through the UK winter is a well-supported, safe dose for most adults.

Vitamin D + K2: The Missing Pair

Vitamin D increases calcium absorption from food. Vitamin K2 (MK-7) directs that calcium into bones rather than soft tissues and arteries. Taking D3 without adequate K2 may lead to calcium being deposited in the wrong places over time.

None of the products listed here include K2. Consider adding a separate K2 supplement (90-200mcg MK-7 daily) or choosing a combined D3+K2 product. Several exist from BetterYou and Solgar.

Who Each Product Suits

Boots Own-Brand (400 IU) — only useful if you get regular sun exposure and just want minimal insurance. Inadequate for most UK residents in winter.

Holland & Barrett (1000 IU) — a step up. Reasonable for summer maintenance when you get some sun.

Myprotein D3 (2500 IU) — best value and a solid year-round dose for active individuals. Softgel format aids absorption.

BetterYou Spray (3000 IU) — good for people who dislike swallowing tablets or have digestive issues. Slightly premium priced.

Solgar D3 (4000 IU) — the highest dose here. Appropriate for winter months, deficient individuals, or those with higher body weight (vitamin D is sequestered in fat tissue). Quality brand with good formulation.

Where to Buy

For full dosing guidance and research, see our vitamin D guide.