Vitamin D in South Africa: why sunshine is not always enough

It seems unlikely that anyone in South Africa could be short of vitamin D. Yet studies in several South African groups have found low levels to be common, particularly at the end of winter. Sunshine is the main source of vitamin D, but getting enough of it depends on much more than living somewhere sunny.

What vitamin D does

Vitamin D helps your gut absorb calcium and phosphate, which your bones need to stay strong. Severe, long-standing deficiency causes rickets in children and soft, painful bones in adults, known as osteomalacia. Milder deficiency is linked with bone loss and a higher risk of fractures in older people, and with muscle weakness.

Vitamin D has been studied for many other conditions, from infections to heart disease to low mood. For most of these, large trials in healthy adults have not shown clear benefits from supplements. Its best-proven role is still in bone and muscle health.

Why sunshine is not always enough

Your skin makes vitamin D when it is exposed to a specific kind of ultraviolet light called UVB. How much you make depends on several things.

• Season and latitude. In winter the sun sits lower and less UVB reaches the ground. This matters most in the southern parts of the country, including Cape Town, where winter vitamin D production is limited.
• Time of day. UVB is strongest around midday. Early morning and late afternoon sun makes much less vitamin D.
• Skin tone. Melanin protects the skin from UV, so darker skin needs longer in the sun to make the same amount of vitamin D.
• Indoor life. Office work, long commutes and screen time mean many people rarely have bare skin in midday sun.
• Clothing and sunscreen. Both reduce vitamin D production, and both are important for protecting your skin.
• Age. Older skin makes vitamin D less efficiently.
• Body weight. Vitamin D is stored in fat, so people with a higher body weight tend to have lower blood levels.

Some health conditions also lower vitamin D. These include coeliac disease and other problems with absorption in the gut, kidney and liver disease, weight-loss surgery and some medicines, such as certain anti-epilepsy drugs.

What the test measures

The blood test measures 25-hydroxy vitamin D, the form that circulates in the blood and reflects your stores over the past few weeks. South African labs usually report it in nmol/L. Some reports and websites use ng/mL instead. To convert, multiply ng/mL by about 2.5, so 20 ng/mL is about 50 nmol/L.

The ranges LifePrint uses

Experts do not fully agree on the right cut-offs for vitamin D. LifePrint uses the bone health thresholds from the Institute of Medicine 2011 report.

• Below 30 nmol/L: deficient.
• 30 to 50 nmol/L: at risk of inadequacy. LifePrint reports this as a grey zone.
• 50 nmol/L and above: sufficient for most people.
• Above 125 nmol/L: potential for harm.

In 2024 the Endocrine Society withdrew its own earlier thresholds and chose not to set new ones. Its review found no clear benefit from raising levels above about 50 to 60 nmol/L in healthy adults. That supports the idea that more is not always better.

When vitamin D is too high

You cannot overdose on vitamin D from the sun, but you can from supplements. Levels above 125 nmol/L are usually the result of taking high doses for a long time. Very high levels can raise blood calcium, causing nausea, thirst, confusion and kidney problems. If your level is high, tell your doctor what supplements you take, including multivitamins and fortified products.

Getting a useful result

Vitamin D changes with the seasons, so your result reflects the time of year you test. A level taken at the end of summer will usually be higher than one taken in August. If you are tracking your level over time, testing in the same season each year makes the numbers easier to compare.

High-dose biotin can interfere with some vitamin tests, so pause it for 48 hours before your draw. Vitamin D itself does not need fasting.

What happens next

Your LifePrint report places your vitamin D in one of the bands above, explains what it means for you and flags how urgently to follow up. A result in the grey zone is common and is rarely urgent. A deficient or very high result is worth discussing with a registered healthcare practitioner, who can look at your risk factors and advise on treatment and when to recheck.