What’s On the Shelves? Understanding Vitamin D Supplements

Which forms absorb best, why vitamin D matters more than most people realize, and how to choose wisely.

Vitamin D may be one of the most misunderstood supplements on the shelf today.

People hear:

• “Take vitamin D.”

• “Everyone is deficient.”

• “Take more in winter.”

• “You need K2.”

• “Get sunshine.”

• “Vitamin D is dangerous.”

• “Vitamin D is essential.”

The confusion is endless.

This article is designed to help cut through the noise and explain:

• what vitamin D actually does

• the difference between D2 and D3

• why magnesium and MK-7 matter

• how vitamin D is absorbed

• signs of deficiency

• how blood testing works

• what forms are usually best absorbed

• why quality matters more than hype

• 
  

The best vitamin D supplement is not necessarily the most expensive one.

The best form is the one your body can absorb and properly utilize.

What Is Vitamin D?

Vitamin D is classified as a fat-soluble vitamin, but many researchers and practitioners also describe it as functioning more like a hormone within the body. So, it is both a vitamin and a hormone.

It influences:

• calcium regulation

• bone metabolism

• immune function

• nervous system signaling

• muscle function

• mood

• inflammation regulation

• energy

• resilience and recovery

Vitamin D receptors are found throughout the body, which helps explain why deficiency may affect so many systems at once.

Why Vitamin D Deficiency Is So Common

Vitamin D insufficiency is extremely common in modern society.

Contributing factors may include:

• indoor lifestyles

• less direct sunlight exposure

• northern climates

• winter months

• sunscreen use

• aging

• darker skin tones

• obesity

• processed food intake

• poor dietary intake

• digestive absorption issues

People living in less sunny climates often require supplementation for at least part of the year.

Older adults also produce less vitamin D through the skin than younger individuals and supplementing is usually required.

IMPORTANT NOTE: Vitamin D insufficiency is widespread worldwide, with research suggesting that nearly half of the global population may have suboptimal vitamin D levels depending on the blood level threshold used. The remedy is blood testing to determine levels and supplementation.

How Vitamin D Is Naturally Produced

Vitamin D synthesis begins when ultraviolet B (UVB) rays from sunlight strike the skin.

The body then begins converting cholesterol compounds within the skin into vitamin D precursors, which are later processed through the liver and kidneys into active forms the body can use.

Brief, sensible sun exposure may support natural vitamin D production depending on:

• season

• latitude

• time of day

• amount of skin exposed

• age

• skin tone

Many people today receive very little direct sunlight due to indoor lifestyles, clothing coverage, sunscreen use, and long winters.

Vitamin D2 vs Vitamin D3

This is one of the most important distinctions consumers should understand.

Vitamin D2 (Ergocalciferol)

Vitamin D2 is typically derived from plant or fungal sources.

It is commonly found in:

• fortified foods

• some mushrooms exposed to UV light

• certain supplements

  
  

Vitamin D2 may raise blood levels temporarily but is generally considered less effective at maintaining optimal vitamin D status long term.

Vitamin D3 (Cholecalciferol)

Vitamin D3, also known as cholecalciferol, is generally considered the preferred and more bioavailable form.

Benefits of D3:

• better absorbed

• more effective at raising blood levels

• longer lasting within the body

• more closely resembles the form naturally produced through sunlight exposure

Most high-quality vitamin D supplements today use D3 rather than D2.

Where Vitamin D3 Comes From

Many people are surprised to learn that most vitamin D3 supplements are derived from lanolin, a waxy substance naturally found in sheep’s wool.

The lanolin is purified and processed into cholecalciferol.

Some vegan vitamin D3 supplements are derived from lichen instead.

Why Absorption Matters

Vitamin D is fat-soluble.

This means the body absorbs it best when:

• taken with food

• consumed alongside healthy fats

• delivered in oil-based forms

  
  

Soft gels and liquid drops suspended in oil are generally absorbed more effectively than dry powder capsules or compressed tablets.

This is one reason many practitioners prefer:

• softgels

• oil-based drops

• under-the-tongue liquid preparations

  
  

Vitamin D supplements are commonly suspended in:

• olive oil

• MCT oil

• sunflower oil

• other carrier oils

  
  

What About Sublingual Vitamin D?

Some vitamin D products are designed to be dropped under the tongue.

These liquid forms may be:

• easier to swallow

• convenient

• rapidly absorbed

They are often available in flavored forms such as peppermint or citrus.

Why Magnesium Matters

Vitamin D does not work alone.

Magnesium is necessary for proper vitamin D metabolism and utilization within the body.

Without adequate magnesium, the body may struggle to properly activate and utilize vitamin D.

This is one reason magnesium deficiency and vitamin D deficiency often overlap.

Many people benefit from supporting magnesium levels alongside vitamin D supplementation.

You can read more about magnesium forms and absorption in my article, ‘What’s On the Shelves? Understanding Magnesium Supplements' found in my blog posts.

Why Vitamin K2 MK-7 Matters

Vitamin K2 helps regulate calcium placement within the body.

This is important because vitamin D increases calcium absorption.

Vitamin K2, especially the MK-7 form, helps support proper calcium utilization by helping direct calcium toward:

• bones

• teeth

rather than allowing excess calcium deposition within soft tissues.

What Is MK-7?

MK-7 is a highly bioavailable and longer-acting form of vitamin K2 commonly paired with vitamin D3 in higher-quality supplements.

Some supplement manufacturers specifically highlight MK-7 on the label because it is considered a preferred form of K2.

Vitamin D and Calcium Balance

Vitamin D plays a major role in calcium absorption and regulation.

Without adequate vitamin D, calcium absorption may be impaired.

However, calcium balance matters.

The body must properly regulate:

• how much calcium is absorbed

• how calcium is utilized

• where calcium is deposited

Calcium is also available through real food sources such as:

• sardines

• canned salmon with bones

• sesame seeds

• parsley

• yogurt

• kefir

• aged cheeses

• leafy greens

• mineral-rich foods

  
  

Mineral-rich foods generally include minimally processed whole foods naturally containing higher levels of important minerals needed for structural, muscular, nervous system, and metabolic health.

Examples include:

• leafy greens

• seeds

• nuts

• legumes

• seafood

• bone-in fish

• quality dairy

• mineral-rich water

• organ meats

  
  

Foods Naturally Containing Vitamin D

Food sources of vitamin D include:

• cod liver oil

• salmon

• sardines

• egg yolks

• liver and organ meats

• fortified foods

• some UV-exposed mushrooms

  
  

However, dietary intake alone is often not enough for many individuals to maintain optimal vitamin D levels year-round.

Signs of Vitamin D Deficiency

Low vitamin D levels may contribute to:

• fatigue

• low mood, feeling down

• frequent illness

• poor immunity

• muscle weakness

• bone discomfort

• poor recovery

• low energy

• generalized aches

• low resilience

• hair shedding in some individuals

Some people simply feel run down and depleted.

What People Often Notice Once Vitamin D Becomes Systemic

With consistent use and improved blood levels, many people report:

• better mood

• improved energy

• stronger immunity

• improved resilience

• less fatigue

• improved muscular function

• better recovery

• improved overall well-being

Benefits often develop gradually over time rather than overnight.

Blood Testing for Vitamin D

The most common blood test for vitamin D is: 25-hydroxy vitamin D [25(OH)D]

Many practitioners consider blood testing the best way to evaluate vitamin D status.

Some healthcare providers routinely include vitamin D testing during annual bloodwork, while others may not test unless specifically requested.

Monitoring blood levels can help guide:

• dosing

• duration of supplementation

• long-term maintenance needs

  
  

How Much Vitamin D Do People Commonly Take?

Needs vary considerably depending on:

• climate

• season

• body composition

• sun exposure

• absorption

• overall health

• blood levels

Many adults commonly supplement within a range of approximately:1,000–5,000 IU daily

A common maintenance amount for many adults is: 2,500 IU daily (or 62.5 mcg)

Higher doses should generally be used only under practitioner supervision with periodic blood testing.

Can You Take Too Much Vitamin D?

Yes.

Excessive vitamin D intake over time may contribute to problems related to calcium dysregulation.

Potential symptoms may include:

• nausea

• weakness

• excessive thirst

• digestive upset

• abnormal calcium levels

If excessive intake is suspected, supplementation should be stopped and blood levels rechecked.

Long-term high-dose vitamin D supplementation is generally not recommended without practitioner supervision and periodic laboratory monitoring.

What’s On the Shelves? Choosing Wisely

When choosing a vitamin D supplement, look for:

• Vitamin D3 (cholecalciferol)

• oil-based softgels or liquid drops

• inclusion of vitamin K2 MK-7

• reputable manufacturers - GMP Certified

• appropriate dosing

• products designed for absorption

In many cases, the best vitamin D supplement is simply the one your body can absorb and consistently utilize.

Final Thoughts

Vitamin D may be one of the most important foundational nutrients in modern wellness.

Understanding:

• forms

• absorption

• dosing

• blood testing

• magnesium support

• vitamin K2

• sunlight exposure

can help simplify the overwhelming amount of information surrounding supplementation today.

If you are overwhelmed by the number of vitamin D products on the shelf, I offer professional supplement guidance and wellness consultations designed to help individuals simplify supplementation and focus on what is truly necessary.

You can also explore professionally selected supplement options through my professional supplement dispensary.

Watch for more “What’s on the Shelves?” articles coming soon, where we continue cutting through confusion and simplifying supplements, wellness products, and ingredients including magnesium, probiotics, fish oil, collagen, electrolytes, calcium, protein powders, and more.

In good health,

Jane A. Thomas

Traditional Naturopath

Master Herbalist