According to a 2023 study by Tata 1mg involving more than 2.2 lakh people conducted across 27 cities, 76% were found to be deficient in this essential vitamin. Vitamin D is important for our bodies because it helps maintain bone health, immune function, and overall well-being.
When we expose our skin to sunlight, our bodies naturally produce vitamin D, making it essential to step out during the day. But, how do you know if your body is absorbing enough sunlight? Dr Vishakha Shivdasani, in a podcast hosted by Raj Shamani, says that there’s a simple way to tell.
She suggests looking at your shadow. If your shadow is shorter than your height when you’re outdoors, it usually means your body is absorbing vitamin D effectively. However, if your shadow appears taller than you, it might indicate that you’re not absorbing enough vitamin D.
Dr Gunasekar Vuppalapti, senior aesthetic and reconstructive plastic surgeon at GVG Invivo Hospital explains, “The length of your shadow compared to your height can give an indirect clue about the angle of the sun in the sky. When your shadow is shorter than your height, it generally means the sun is high in the sky, typically above a 45-degree angle from the horizon. This position is crucial for the UVB rays from the sun to penetrate the atmosphere effectively and reach your skin, which is necessary for the synthesis of vitamin D.”
During times when your shadow is shorter than your height, he elaborates, your body is more likely to produce vitamin D optimally because the sun’s UVB rays are at their strongest. This typically occurs during the midday hours around solar noon between 10 am to 3 pm. However, the duration of exposure and the body surface area exposed are equally important.
Dr Gunasekar Vuppalapti, senior aesthetic and reconstructive plastic surgeon at GVG Invivo Hospital explains, “The length of your shadow compared to your height can give an indirect clue about the angle of the sun in the sky.” (Source: Freepik)
What factors influence the length of the shadow in this context?
“The shadow test is based on the understanding that UVB rays, which are responsible for skin synthesis of vitamin D, are most abundant when the sun is at least 45 degrees above the horizon,” Dr Vuppalapti says. If the sun is lower, much of the UVB is absorbed or reflected by the earth’s atmosphere.
The length of a shadow, he adds, is influenced by the sun’s position relative to an object. Early in the morning and late in the afternoon, the sun is lower, making shadows longer. Near solar noon, when the sun is at its highest point, shadows are much shorter. This simple observation helps indicate the potential for effective vitamin D synthesis.
What are the implications if my shadow appears taller than my height when I’m outdoors? Does this always mean I am not absorbing enough vitamin D?
Taller Shadow and Vitamin D Synthesis: If your shadow appears taller than your height, it typically indicates that the sun is at a lower angle (below 45 degrees). During these times, Dr Vuppalapti says that the effectiveness of UVB radiation in reaching your skin is reduced, which can decrease vitamin D synthesis.
Other Factors: “While a taller shadow can indicate suboptimal conditions for vitamin D absorption, it’s not a definitive measure,” he remarks. Cloud cover, air pollution, and geographical factors also influence UVB exposure. Additionally, skin type, age, and the actual skin area exposed to sunlight are crucial for vitamin D synthesis.
Factors that might affect the reliability of using the shadow test
*Time of day and weather conditions: Dr Vuppalapti agrees that the reliability of the shadow test can vary. Near midday (between 10 AM and 3 PM), especially during summer months, the test is most reliable due to the higher position of the sun. However, during early morning, late afternoon, or non-summer months, the sun’s angle may not be adequate regardless of a shorter shadow.
*Effect of weather and location: “Overcast skies, high latitude, and seasons significantly affect UVB availability,” he informs. For example, in higher latitudes during the winter months, he suggests, even a short shadow at midday might not correspond with effective vitamin D synthesis due to the low intensity of UVB rays.