More vitamin D reduces the risk of many serious diseases

Summer sunlight is vital and is the primary source of vitamin D, which plays a crucial role in bone health, immune function, brain activity, mood, circulation, cancer prevention, kidney function, blood sugar regulation, muscle strength, pregnancy, and fetal development. However, to achieve the optimal effect, the level of vitamin D in the blood must be higher than the officially recommended minimum values. This is the conclusion of a review article published in Nutrients, where researchers also discuss how much vitamin D is needed to optimize blood levels of the nutrient.

Official recommendations for vitamin D intake primarily aim to support bone health and prevent rickets. Most of the body’s cells have receptors for vitamin D, which helps regulate around 10 percent of our genes. However, current guidelines do not account for the many metabolic processes in which vitamin D is involved.

According to the new review article, 27 international researchers refer to a range of randomized controlled trials (RCTs) showing that vitamin D reduces the risk of infections, cancer, type 2 diabetes, impaired muscle function, and autoimmune diseases such as rheumatoid arthritis and multiple sclerosis.

Conversely, vitamin D deficiency increases the risk of these conditions. It also raises the likelihood that infections like COVID-19 or influenza become life-threatening, or that cancer becomes fatal.
Since the strong summer sun is our primary source of vitamin D, it is no coincidence that mortality rates are much higher in the early months of the year compared to late summer, when many people’s vitamin D levels peak. During the winter, many also experience joint pain, depression, fatigue, unstable blood sugar, and other symptoms that occur when vitamin D levels decline due to depleted liver stores.

The need for vitamin D often exceeds official recommendations

According to the review article, vitamin D deficiency is a global health issue affecting around 45 percent of the population, especially at northern latitudes where sunlight is limited.
Inconsistent results from vitamin D supplementation studies can often be explained by the use of too low doses or too short study durations, which prevent blood levels from reaching optimal ranges.

The official guidelines for vitamin D requirements also appear to be too low, typically ranging from 5-20 micrograms daily, with higher amounts recommended only for older or vulnerable individuals. Similarly, the official lower limit for blood vitamin D levels (50 nmol/L (20 ng/mL)) seems insufficient for protecting against the wide range of metabolic disorders and diseases.
In the review article, the researchers refer to a number of population studies showing that higher blood levels of vitamin D reduce the risk of common and serious diseases, including pregnancy complications that can affect child development.
They recommend that blood levels of vitamin D should exceed 75 nmol/L (30 ng/mL), which is usually achievable with a daily supplement of 50 micrograms.
A daily supplement of 100-150 micrograms can raise blood levels to between 100-175 nmol/L (40-70 ng/mL), and according to the researchers, these higher levels may offer even stronger protection against cancer and other serious diseases.

For this reason, the researchers recommend routine vitamin D level measurements in the population as part of an effort to prevent and treat a wide range of health conditions.
They also call for more large-scale population studies to help fine-tune recommendations for both vitamin D supplementation and optimal blood levels.

For reference, the European Food Safety Authority (EFSA) has set an upper daily intake limit for vitamin D supplements at 100 micrograms. However, most people with fair skin can produce significantly more than this on a hot summer day.
The upper limit for blood levels of vitamin D is set at 160 nmol/L. But according to the new review article, there are strong indications that current recommendations for vitamin D supplementation and blood level targets should be revised and updated.

References:

William B Grant et al. Vitamin D: Evidence-Based Health Benefits and Recommendations for Population Guidelines. Nutrients 2025