Vitamin D Deficiency: Fact-file by Dr Deepak Hiwale

‘Each day, Apollo’s fiery chariot makes its way across the sky, bringing life-giving light to the planet. For the ancient Greeks and Romans, Apollo was the god of medicine and healing as well as of sun and light—but Apollo could bring sickness as well as cure. Today’s scientists have come to a similarly dichotomous recognition that exposure to the ultraviolet radiation in sunlight has both beneficial (prevents obesity and metabolic disorders) and deleterious effects (sunburn, skin cancer) on human health.’– M. Nathaniel Mead

Vitamin D Deficiency: Fact-file by Dr Deepak Hiwale

As way back, as the mid-1920s, Windaus et al. suggested that skin, when exposed to sunlight, produced the active form of Vitamin D (D3) from a cholesterol precursor – 7-dehydrocholesterol (Holick, 2016).

Synthesis in the skin is the major source (up to 90%) of Vitamin. D (VIT D) in humans. Lack of appreciation that sun exposure is the major source, is the primary reason why VIT D deficiency is now a worldwide epidemic! Very few foods contain enough VIT D; foods fortified with VIT D aren’t of much use either: often inadequate to satisfy even a child’s (let alone an adult’s) VIT D requirement!

What is Vitamin D? And, what does it do?

Vitamin D is a master hormone rather than just a vitamin per se – has multi-system functions. Few of these are:

  • Calcium-bone metabolism, nerve impulse generation & conduction
  • Functioning of the muscle, heart, pancreas and endocrine organs
  • Strengthens immunity, fights infections including TB
  • Plays a role in cancer prevention – lung, colon, and breast, to name a few

Vitamin D Deficiency

VIT D deficiency has a worldwide prevalence; it underpins the aetiology (cause) of several chronic metabolic-endocrine disorders, including obesity. Researchers define deficiency as 25(OH)-VIT D blood levels of < 20 mg/mL; blood level of 25-

hydroxyVit. D of >75 nmol/L, or 30 mg/ml is required for optimal health.

IsVIT D deficiency a problem? Yes indeed; because deficiency ofVIT D may increase the risk of (Source: Pereira-Santos M. et al., 2015):

  • Osteoporosis (thinning of bones), and therefore increased risk of fractures,
  • Osteoarthritis,
  • Metabolic disease including obesity, diabetes, hypertension, and several autoimmune diseases/ disorders,
  • Infections – VIT Ddeficiency compromises functioning of immunity and therefore, may increase risk of the individual to infections,
  • Psychiatric disorders (mainly, depression), and
  • Cancers – those exposed to more sunlight during their lifetimes are less likely to die of cancers. Cancer-related death rates decline as one moves toward the lower latitudes (between 37°N and 37°S)

VIT D Deficiency and Obesity

Obese individuals exhibit 35% greater prevalence of VIT D deficiency compared to leaner ones. It is suspected that obese individuals – owing to the social stigma attached with being obese – are more likely to reduce their exposure to sunlight, perform fewer outdoor activities and/or use clothes that cover much of the body; this limits the exposure to sun and consequently, hampers cutaneous (skin) VIT D synthesis.

How low VIT D levels favour Obesity

  • Increased metabolic clearance of VIT D possibly with enhanced uptake by fat tissue (VIT D is fat-soluble), leaving little in the plasma to do its job
  • Increased differentiation of pre-adipocytes (immature fat cells) into adipocytes (mature fat cells) capable of storing fat
  • Increased inflow of calcium into fat cells, leading to increased fat production
  • Increased secretion of parathyroid hormone, shown to be linked to obesity

Sources of VIT D

80-90% of VIT D present within the human body originates from skin synthesis where sunlight activation plays a key role; rest is supplied through food or supplementation (these sources absolutely pale in comparison to sunlight!).

Sunlight as a Source of VIT D

Synthesis in the skin – secondary to exposure to sunlight - remains the major source (up to 90%) of VIT D in humans. Lack of appreciation that sun exposure is the major source, is the primary reason why VIT D deficiency is now a worldwide epidemic!  The recommendations for the avoidance of all sun exposure due to risk of skin cancer has put the world’s population at risk of VIT D deficiency. 

Daily solar exposure – to maintain physiologically effective serum levels – 15 minutes in summer and 20 minutes in early fall or late spring is recommended; coloured people require twice as long.Interestingly, from November to March, in countries north of 37° latitude regions, no amount of solar exposure is sufficient!

In individuals who tend to burn easily / tan poorly, exposure to sun should not exceed 20 minutes per day; exposure longer than 20 minutes does not further increase VIT D synthesis but could increase risk of skin cancer!

Food Sources of VIT D

Few foods contain VIT D; foods fortified with VIT D are also an alternative.

  • Fatty Fish: tuna, mackerel, salmon, sardines (and caviar), fish Oils: Cod liver oil
  • Eggs (yolk), milk, cheeses, fortified dairy products and orange juices
  • Mushrooms

Pharma Sources

Oral VIT D3 supplementation rather than solar exposure, should be used by fair-skinned, sun-sensitive individuals.

As mentioned earlier, blood level of 25-hydroxyVit. D of >75 nmol/L, or 30 mg/ml is required for optimal health. In the absence of adequate sun exposure, supplementation with 800-1000 IU VIT D/day is needed to achieve the above levels. Pharmaceutical form of VIT D in the US is VIT D2; in Canada, Europe, Japan and India, VIT D3.

Most of us have low vitamin D levels. A recently published study shows that, this is likely due to a genetic predisposition and that low vitamin D may not necessarily be a problem; low VIT D or low calcium intake are not associated with increased fracture risk, say the authors. In short, for most of us, there’s no need for VIT D-calcium supplementation! Also, do not forget that VIT D- Calcium supplementation has no/minimal benefits but may pose health risks!

Take Home Messages

  • Lack of physiological blood levels of VIT D can cause health problems
  • Almost 90% of VIT D present in the human body come from synthesis in the skin after exposure to sunlight
  • Sunlight exposure remains your best bet to keep VIT D levels within physiological ranges to avoid diseases or disorders
  • Sunlight exposure of 15 minutes in summer and 20 minutes in early fall or late spring is recommended; coloured people require to be twice as long in the sun.


  1. Catherine Shore-lorenti et al, Clinical Endocrinology (2014) 81, 799-811
  2. Garland et al., Am J Public Health. 2006 Feb;96(2):252-61
  3. Nathaniel Mead, Environmental Health Perspectives. April 2008; 11(4)
  4. Pereira-Santos et al., Obesity Reviews. April 2015; 16(4):341–349
  5. Michael M. Holick, Anticancer Res. 2016 Mar;36(3):1345-56
  6. Michael F Holick and Tai C Chen, Am J ClinNutr 2008;87(suppl): 1080S-6S.
  7. Katerina Trajanoska et al., BMJ. 29th. Aug., 2018

About The Author

Dr. Deepak Hiwale

Dr. Deepak specialises in Sports & Exercise Medicine. He has previously worked in the UK (with top athletes, as well as reputed personalities from the entertainment industry.. Read More..


Recent Comments

Leave Comments