VEGANALYZE

Vitamin D Requirement Per Day

Vitamin D is primarily needed for the absorption of calcium from food, body development, growth, and maintenance of the skeleton 1. Therefore, supplying the body with vitamin D in the "right" amounts is enormously important for health. Since vitamin D deficiency is a worldwide problem, it is extremely relevant to consider the current intake recommendations and adjust the diet accordingly. Nonetheless, about 90% of the required vitamin D is formed through exposure of the skin to sunlight 2. Therefore, it is very important to replenish vitamin D reserves during the summer months. In the winter months, no vitamin D can be formed anymore due to the low angle of incidence of the sun's rays in our latitudes 3. During this time, it is particularly important to rely on foods rich in vitamin D.

Requirements

There are numerous vitamin D intake recommendations that vary from country to country 4.

The following amounts of vitamin D should be consumed in the USA when endogenous synthesis (the production of vitamin D through the skin) is lacking 5:

Conversion: 1 µg = 40 IU and 1 IU = 0.025 µg

Further recommended intakes depending on the country can be found here 6.

To increase plasma levels of 25-hydroxyvitamin D [25(OH)D] by 1 ng/ml (2.5 nmol/L), an additional 100 IU of vitamin D per day is required. 7.

More vitamin D may be needed

However, scientists consider the current intake recommendations inadequate to address the growing epidemic of vitamin D deficiency 8. Therefore, they consider 800 to 1,000 IU per day to be appropriate for most age groups, especially to prevent osteoporosis and rickets 9 10 11. The Endocrine Society goes even further and has issued the following recommended daily intakes 12:

Vitamin D Requirement for Athletes

Scientists recommend athletes to strive for an increased consumption of Vitamin D. Athletes should aim for plasma concentrations of 25(OH)D in the range of ≥32 ng/mL (80 nmol/L) - preferably ≥40 ng/mL (100 nmol/L) 13. According to studies, these levels can be achieved through regular and safe sun exposure (2x a week between 10 am and 3 pm on the arms and legs for 5-30 minutes, depending on season, latitude, and skin pigmentation) or through a Vitamin D supplementation of 1,000 to 2,000 IU per day 14.

Obese individuals have a higher requirement

Even obese people need more Vitamin D because it is quickly stored in fat tissue, making it unavailable to the body at the current time (Vitamin D gets masked). Obese children and adults need twice as much Vitamin D as normal weight individuals 15. Study results with Vitamin D supplements have shown that obese people achieved much lower plasma concentrations of 25-Hydroxyvitamin-D with the same oral dosage compared to normal weight individuals 16.

How to meet daily needs?

Sunlight has long been recognized as a major provider of vitamin D for humans. Radiation in the UVB (290-315 nm) portion of the solar spectrum photolyzes 7-dehydrocholesterol in the skin to previtamin D3, which, in turn, is converted by a thermal process to vitamin D3 17.

The daily vitamin D requirement of about 15 µg (600 IU) can be met in the summer months with about 5 to 15 minutes of sunlight on the skin between 10 am and 3 pm, without using sun protection 18. During the winter months, whether UVB still reaches the skin or not depends heavily on the latitude. During the months of November through February in Boston (latitude 42.2 degrees N), exposing human skin to sunlight on cloudless days did not result in the production of previtamin D3. In Edmonton (latitude 52 degrees N), this period of ineffective vitamin D synthesis extended from October through March. However, in locations farther south (latitude 34 degrees N and 18 degrees N), such exposure to sunlight during the middle of winter was effective in converting 7-dehydrocholesterol to previtamin D3 19.

This often leads to a vitamin D deficiency during this time. Therefore, it is particularly important in the winter months to rely on plant-based foods with vitamin D, vitamin D-fortified foods, drinks or vitamin D supplements or supplements (to be discussed with your family doctor).

With a vegan diet, meeting the requirement is slightly more difficult as vitamin D is only found in a few plant-based foods (list).

For completeness, we would like to mention that, in addition to sunlight and a vitamin D-rich diet, there are also UVB lamps and light bulbs for vitamin D formation 20. However, these should only be used in consultation with your family doctor. Special UVB irradiation options are often available in tanning studios as well.