Part 33: Vitamin D Adequacy: A Cost-effective Public Health Approach for Preventing Disease

This article is supplementary to a previous Article 32, on vitamin D in this series and provides additional information, as requested by several readers. 

Vitamin D deficiency:

Vitamin D deficiency is common in all age groups. The prevalence of vitamin D deficiency is widespread in most countries but is grossly underestimated. It is a major global public health problem; it is, in fact is a pandemic that threatens more than one-third of the world’s population. It affects all ages, genders, and ethnic groups. 

Vitamin D is an essential micronutrient that is generated in the skin after exposure to ultraviolet B (UVB) rays; however, most people do not receive adequate exposure to the sun's’ rays. Following UV exposure, 7-dehydrocholesterol present in the skin is photo-converted to form previtamin D. Subsequently, previtamin D isomerizes to form vitamin D, and is transported to the liver via the bloodstream.

How do humans obtain vitamin D?

Vitamin D synthesis in the skin and is affected by many factors, including the condition of the skin (e.g., scarring, aging, etc.); the density of melanin in the skin—darkness of the skin; and exposure to sun (duration, time of the day, and the time of the year of exposure). Once vitamin D reached the liver, it undergoes two activation steps. First, in the liver, it is activated to 25-hydroxyvitamin D [25(OH)D], and then in the kidneys, 25(OH)D is further activated (hydroxylated) to form its potent steroid hormonal form, 1,25(OH)2D, which is an obligatory hormone for optimal physiological activities and maintenance of a healthy life.

Sun UVB exposure:

Despite the availability of adequate sunlight throughout the year in many parts of the world, many people continue to be vitamin D deficient. The reasons for such deficiency include geographic locations, such as living far from the equator (in higher and lower latitudes); sun-avoidance behavior; the overuse of sunscreens that block UVB rays (290–315 nm spectra); the health of an individual’s skin; the use of medications that enhance the breakdown of vitamin D; and gastrointestinal absorption issues. While, shorter wavelengths, around and below 295 nm are the most effective in producing vitamin D, a significant amount of UVB less than 295 nm and UVA rays are filtered by the atmospheric ozone layer. 

Does the use of sunscreens prevent generation of vitamin D in the skin?

Commercially available sunscreens with a sun protection factor (SPF) greater than 12, block UV rays from reaching the skin. These sunscreens primarily block UVA rays (which account for more than 90% of solar radiation) but UVB rays are blocked to a lesser extent especially by sunscreens with a high UVA-protection factor. Thus, the use of sunscreens may still allow some UVB rays to reach the skin (dermis) to generate a small amount of vitamin D.

A recent review concluded that daily and recreational use of sunscreen photoprotection does not compromise vitamin D synthesis, even when the sunscreen is applied under optimal conditions. Another cent study concluded that, sunscreens may be used to prevent sunburn, while allowing vitamin D synthesis in the skin. The use of high UVA-PF sunscreen enables significantly higher vitamin D synthesis than does a low UVA-PF sunscreen because the former, by default, transmits more UVB than does the latter. These two statements are similar to the recommendation made in the next section.  

Recommendations for safe sun exposure:

Many individuals avoid sun exposure and consequently become vitamin D deficient. Thus, a practical recommendation is to allow sun exposure for 15 to 25 minutes and then apply a sun-blocking cream/ointment with an SPF greater than 20 to circumvent erythema, sunburn, photo aging of the skin, and possibly skin cancer in later life. Those who are unable to adhere to such recommendations because of lack of sunlight or cultural or medical reasons should consider vitamin D supplementation in recommended dosages.

What is an adequate level of vitamin D in the blood?

As described previously (in Article 32), vitamin D status is determined by measuring the serum 25(OH)D concentration [not by measuring 1,25(OH)2D]. 25(OH)D is a sensitive biomarker and the only means of determining vitamin D sufficiency or deficiency. The minimum blood level for vitamin D sufficiency is 30 ng/mL (75 pmol/L). However, a handful of guidelines, such as those of the Institute of Medicine, suggest that 20 ng/mL (50 nmol/L) is a sufficient blood level; this, however, is not accepted by most scientists.

Values of less than 20 ng/mL are adequate only for preventing osteomalacia (and bone mineralization) but not for controlling infections, metabolic disorders, cancer, or autoimmune diseases. Thus, levels below 20 ng/mL have little beneficial effect on extraskeletal disorders that are worsened by vitamin D deficiency, and thus, should not be considered as the minimum healthy level.

The goal should be to reach a sustainable blood (serum) level of 25(OH)D above the minimum concentration of 30 ng/mL (optimal range is between 30 and 60 ng/mL). Most people, unless regularly exposed to sunlight between the hours of late morning to mid-afternoon, would be benefited by a daily maintenance dose of a vitamin D3 supplement (practical aspects of vitamin D supplementation is discussed in the next article).

Requirements of vitamin D:

During the first year of life, infants need at least 400 IU of vitamin D per day, and the requirement gradually increases to 1,000 IU/day. Most healthy adults require an intake of 1,000 to 2,000 IU/day, and most elderly individuals need an additional 2,000 IU/day. Those with disorders that affect vitamin D generation or who have enhanced catabolism of vitamin D for any reason need much higher doses to maintain optimal health. Except for vegans, vitamin D3, not vitamin D2, is the preferred form of supplement

From the time of ingestion of vitamin D or a reasonable exposure to sun, it takes approximately 3 days to see an increase in 25(OH)D concentration in the blood. Considering the longer half-life, large storage capability, and the time taken to establish equilibrium, serum 25(OH)D concentration should not be rechecked before 12 weeks from the completion of a loading dose. If the blood level is still deficient, a second 6- to 10-week course of higher dose (50,000 IU/week) cholecalciferol (D3) can be prescribed. 

Common causes of vitamin D deficiency:

Except for vitamin-D–fortified foods, sun-exposed mushrooms, and oily fish (including sardines, mackerel, and salmon), foods contain minimal amounts of vitamin D. Thus, diet does not provide an adequate amount of the vitamin to meet daily needs in most people. Consequently, more than 50% of the world’s population is vitamin D insufficient or deficient. 

The most common causes of vitamin D deficiency are (a) insufficient exposure to sunlight, (b) inefficient conversion of ergosterol to vitamin D in the skin, (c) insufficient intake of dietary vitamin D, (d) gastrointestinal abnormalities that hinder vitamin D absorption, (e) increased catabolism of vitamin D (e.g., taking certain medication), (f) failure of activation of vitamin D because of liver or renal disease, and (g) rare genetic diseases that affect absorption, transportation, or activation of vitamin D.

Maintenance of serum 25(OH)D levels:

The amount of vitamin D a person needs daily to maintain a normal serum 25(OH)D concentration depends on several factors, including a person’s skin color, age, sun exposure (time of the day and the season), diet, body storage, and underlying medical conditions, as well as function of the liver and kidneys. The latter two organs are essential for activation of vitamin D. 

Infants, especially those who are exclusively breastfed, should be given nonprescription vitamin D drops containing 400 IU starting within the first few days after birth; the dosage should later be increased to 1,000 IU/day. The use of tanning beds (which provide high doses of both UVB and UVA) is not recommended as a source for vitamin D because of the risk of skin damage and cancer.

Role of vitamin D in human health:

Vitamin D plays many important roles in human health. Its classic actions include calcium homeostasis and development and calcification of bones. Those who are exposed to adequate sunlight and/or consume vitamin-D–fortified dairy products have a low incidence of vitamin D deficiency and associated complications. 

When blood 25(OH)D (and tissue vitamin D) concentrations are maintained in the normal range (i.e., between 30 and 60 ng/mL in serum) several common conditions can be prevented, and their severity are reduced. These conditions/disorders include falls and fractures; autoimmune diseases; cardiovascular diseases; cancer; inflammatory disorders such as microbial infections; and metabolic disorders, such as diabetes, obesity, hypertension, and metabolic syndrome. Let’s briefly look at pregnancy, as one example to illustrate the importance of vitamin D sufficiency.  

Vitamin D in pregnancy:

Maintaining appropriate physiological serum 25(OH)D levels during pregnancy would reduce the incidences and severity of several pregnancy-associated issues, including preeclampsia, cesarean deliveries, premature deliveries, hypertension during pregnancy, as well as premature delivery, small-for-gestation neonates, infant mortality, and minimize several common illnesses during early childhood.  Having 25(OH)D concentrations above 40 ng/mL before and during pregnancy, would substantially reduce these maternal and fetal complications. In addition, maintaining serum 25(OH)D concentrations is essential in the post-pregnancy period and during lactation.

These series of articles are not meant as medical advice. Individuals are expected to consult their own physicians for advice and treatment. Next article discusses the disease prevention strategies using vitamin D sufficiency.

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Professor Sunil J. Wimalawansa, MD, PhD, MBA, DSc, is a physician-scientist, educator, social entrepreneur, and process consultant. He is a philanthropist with experience in long-term strategic planning, and cost-effective investment and interventions globally for preventing non-communicable diseases [recent charitable work]. The author has no conflicts of interest and received no funding for this work.