All you need to know about Vitamin D

Vitamin D is a fat-soluble, hormone-like nutrient manufactured from cholesterol when our skin is exposed to UVB in direct sunlight. Since very few foods contain meaningful amounts of vitamin D, we are dependent on the sunlight to keep our natural vitamin D levels up.essential for bone health, immune regulation, metabolic function, and neurological health. Unlike most vitamins, vitamin D is primarily synthesised in the skin following exposure to UVB sunlight, making deficiency common—especially in individuals with limited sun exposure.

Why Vitamin D Matters

Vitamin D plays a central role in:

• Calcium and phosphorus absorption, supporting bone density, teeth, and muscle function

• Immune modulation, influencing innate and adaptive immune responses.

• Inflammation control, through regulation of inflammatory cytokines. This activity may be important in a number of autoimmune diseases.

• Gut health: plays an important role in maintaining the integrity of the gut lining. It helps support the structures that hold gut cells tightly together, forming a strong protective barrier. This barrier acts like a security filter, allowing nutrients to pass into the bloodstream while preventing harmful or unwanted substances from crossing through the gut wall.

• Neurocognitive and mood regulation, helps regulate normal brain development and function. We have vitamin D receptors on almost every cell in the body, including receptors in the cells of the pre-frontal cortex of the brain, an area of the brain which is critical for mood regulation.

Low vitamin D status has been associated with increased risk of osteoporosis, recurrent infections, autoimmune conditions, cardiometabolic disease, and mood disorders.

Who Is at Risk of Deficiency?

Vitamin D deficiency is highly prevalent worldwide. Individuals at higher risk include:

• Older adults

• Individuals with darker skin pigmentation

• Those who spend little time outdoors

• People living at higher latitudes

• Individuals with malabsorption, obesity, or genetic variations affecting vitamin D metabolism

Diet alone is rarely sufficient to meet requirements, as few foods naturally contain meaningful amounts of vitamin D.

Supplementation: What the Evidence Shows

Vitamin D supplementation is often necessary, particularly during periods of low sun exposure. Research supports:

• Vitamin D3 (cholecalciferol) as more effective than D2 in raising and maintaining blood levels of 25-hydroxyvitamin D

• Typical maintenance doses range from 1,000 IU per day, although some individuals may require higher amounts. Blood test results help determine the most appropriate dose for your specific needs, as supplementation should always be personalised.

Vitamin D and Vitamin K2: A Functional Pair

Vitamin D supports calcium absorption, while vitamin K2 helps direct calcium into bone tissue and away from soft tissues, including blood vessels. This synergistic relationship is important for long-term bone and cardiovascular health.

Note: Vitamin K2 may not be suitable for individuals on anticoagulant medication and should be discussed with a healthcare professional.

Optimising Absorption

As a fat-soluble vitamin, vitamin D is best absorbed when taken:

• With a meal containing healthy fats (e.g., olive oil, avocado, nuts, seeds, oily fish)

• Consistently, to maintain stable blood levels