Vitamin D, often referred to as the “sunshine vitamin,” plays a crucial role in our overall health. This nutrient is particularly worthy of attention as we head into the winter months here in the UK. Government guidelines recommend vitamin D supplementation of 10mg per day between the months of October – April for those aged 4 years and over (1).

In this blog post, we will dive into the following;

  • Background of vitamin D
  • Production and sources of vitamin D
  • Why we need vitamin D to function optimally
  • Populations most at risk of vitamin D deficiency
  • Potential link between vitamin D and obesity
  • Interaction Between Vitamin D & Vitamin K

Vitamin D: A Brief Overview

Vitamin D is a fat-soluble vitamin that can be obtained through two primary sources: sunlight and foods.

Food sources such as oily fish, eggs, liver, mushrooms and fortified* products such as breakfast cereals and plant-based milks. Although these provide a source of vitamin D, it is still very difficult to meet vitamin D requirements through diet alone.

Not all alternative kinds of milk (soya, oat, coconut, almond) are fortified with vitamin D, so make sure to check the ingredients list if you follow a predominantly plant-based diet. If you are following a plant based or vegan diet, get in touch with our team today to ensure you are not at risk of developing any nutritional deficiencies!

When our skin is exposed to sunlight, it produces vitamin D naturally. This process occurs when ultraviolet (UV) rays from the sun interact with a form of cholesterol in our skin, converting it into a precursor of vitamin D (2).

The Role of Vitamin D in Our Body

Vitamin D plays a vital role in maintaining our overall health. The term vitamin D refers to not one compound but many. Vitamin D is also known as calciferol and compromises of groups, some called ergocalciferol (Vitamin D2) and cholecalciferol (Vitamin D3). D2 is largely added to foods, whereas D3 is sourced from the sunlight and animal based foods. Both forms are used in supplements.

One of its primary functions of vitamin D is to facilitate the absorption and utilisation of calcium and phosphorus, which are essential for strong and healthy bones. Without adequate vitamin D, the body cannot effectively absorb calcium, leading to weakened bones and an increased risk of fractures. Vitamin D also helps regulate the immune system and reduce inflammation, making it crucial for optimal immune function (4).

Furthermore, vitamin D is involved in muscle function, helping to maintain muscle strength and prevent muscle weakness. It also has a role to play in supporting cardiovascular health and wound healing, as well as our mood and mental health (5).

People at Risk of Vitamin D Deficiency

  1. Absorption reduction: While vitamin D deficiency is relatively widespread, certain groups of people are more prone to deficiency. Individuals who spend limited time outdoors or those living in northern latitudes with less sunlight, are at higher risk. Darker-skinned individuals are also more vulnerable to deficiency as their skin requires more sun exposure to produce adequate vitamin D (6).
  2. Older Adults: Older adults may have reduced vitamin D production in their skin, making them more susceptible to       deficiency.
  3. Other conditions: People with certain medical conditions, such as inflammatory bowel disease (IBD), coeliac disease, or cystic fibrosis, may have difficulty absorbing vitamin D from food.

The Potential Link Between Vitamin D and Obesity

Emerging research suggests a possible link between vitamin D deficiency and obesity. Several studies have found that overweight and obese individuals tend to have lower levels of vitamin D compared to those with a healthy weight. However, the exact relationship between vitamin D and obesity remains unclear. Theories suggest that adipose tissue (fat cells) may sequester (‘steal’) vitamin D and prevent optimal use in the body. However, further robust research is required to substantiate this hypothesis (7).

Interaction Between Vitamin D & Vitamin K

Vitamin D enhances calcium absorption in the intestines, which is important for bone health. However, if there’s an excess of calcium in the bloodstream due to excessive vitamin D intake and insufficient levels of vitamin K, this can lead to calcium deposits in soft tissues, such as arteries and kidneys, which is something we want to avoid. Vitamin Kis necessary to regulate where calcium is deposited in the body, preventing it from being deposited in the wrong places.

So, whilst adequate vitamin D is needed for calcium absorption, having enough vitamin K is necessary for proper regulation of calcium, ensuring it goes to the right places in the body (our bones) and doesn’t accumulate in places where it can cause harm such as the kidneys and arteries. Therefore, it’s often recommended to maintain an adequate balance of both these vitamins for overall health and to prevent potential complications related to calcium metabolism, which is why some supplements provide both vitamin D3 along with K2(8). However, it’s important to consult with a dietitian and your GP before starting any supplementation, as the appropriate dosages can vary from person to person.


Vitamin D is an essential nutrient that plays a crucial role in various aspects of our health. From bone health to immune function, this family of vitamins helps maintain our overall well-being. It is important to ensure we get enough sunlight exposure, especially during the winter months or in regions with limited sunlight. Incorporating vitamin D-rich foods into our diet, such as fatty fish, fortified dairy products, eggs, and fortified cereals, can help us reach our vitamin D requirements.

For individuals at higher risk of deficiency, such as those exposed to less sunlight or older people, supplementation may be recommended under the guidance of a healthcare professional, of 10mg/day or more. By prioritising our vitamin D intake, we can take a proactive step towards promoting optimal health and preventing potential health complications, including increased fracture risk and immune dysfunction.

*Fortification refers to the addition of nutrients to a product to improve the vitamin or mineral content.

Why not take care of your vitamin D needs this winter and contact our team for a bespoke micronutrient analysis? Reach out to book a free discovery call today!