The main function of Vitamin D is regulating calcium, magnesium, and phosphorus to make our bones and teeth strong.

Scientific studies revealed that vitamin D is essential in preventing other physical diseases such as scurvy, beriberi, rickets, osteoporosis, pellagra, and night blindness (Combs & McClung, 2017). But this so-called “sunshine vitamin” is also hard to find in most natural diets as it limitedly occurs only in a few foods like fortified dairy products, mushrooms, and a few fatty fish such as salmon, sardines, and mackerel (Office of Disease Prevention and Health Promotion, 2015).

Vitamin D also occurs naturally in some fish liver and oils, the richest natural food source of said vitamin apart from sunlight, although they may not be the healthiest choice for those with CKD. It is also found in plant sources: nightshade plant family, such as tomatoes, tomatillos, eggplant, bell peppers and chilli peppers, as well as Gramineae plant family, such as wheat, rye, oat, maize, rice, and bamboo (Combs & McClung, 2017).

But some of these food groups though are not CKD-friendly.

So, what is the simple solution to vitamin D deficiency for those with CKD and the general population, as well? The answer comes effortlessly from Mother Nature herself. Get enough sunlight (Linos, et al., 2012)—do not stay in the shade and wear long sleeves.

There seems to be no consensus among scientists and health agencies as to what is vitamin D’s Recommended Daily Allowance. There is, however, a daily Adequate Intake (AI).

These figures are given assuming that there is no vitamin D produced from sunlight. The AI is set to prevent diseases caused by this vitamin’s deficiency such as those most common: rickets and osteomalacia, or the softening of bones. 

According to the Kidney Disease Improving Global Outcomes guidelines (2017), 25 (OH)D levels should be determined in patients with CKD stages 3 to 5, and if levels are low, physicians should consider vitamin D supplementation.

Vitamin D deficiency and CKD, according to science

Vitamin D deficiency has long been associated with CKD incidence and progression. (Andress, 2006; Banerjee & Jha 2019; Hasegawa, et al., 2010; Junarta, Jha, & Banerjee, 2019; Kovesdy, et al., 2007; Zhang et al 2018). The trend seems to be the more the vitamin D intake, the less the chance of getting or developing CKD.

A 2011 study led by Biggar and other German nephrologists revealed vitamin D’s benefits which are beyond bone metabolism, a continual cycle of bone growth and reabsorption, such as the following:

• Amelioration of left ventricular hypertrophy

• Antihypertensive effects

• Antiproteinuric and renoprotective effects

• Induction of vascular calcification

• Suppression of vascular calcification                  

• Modulation of autoimmunity

• Link to innate immunity and microbial defense

• Anticancer properties (colon, breast, and prostate cancer, lymphoma)

• Protective relationships to: Dementia, Allergy, Aging and cognitive function, Muscular strength, and Mortality

The same study also proposed a “steroid hormone vitamin D replacement therapy” for CKD patients organ protection and bone metabolism. “It might seem prudent”—Biggar and colleagues (2011) further asserted—“to advocate treating CKD patients with a sufficiently high dose of vitamin D.”

Six years after, another study (Jean, Souberbielle, & Chazot, 2017) looked into the association between vitamin D deficiency, or insufficiency, to those with CKD patients in dialysis. Here are the findings:

• Secondary HPT and high bone turnover markers
• Low bone mineral density
• Muscle weakness and risk of falls
• Metabolic syndrome and obesity, insulin resistance
• Left ventricular hypertrophy and atherosclerosis 
• Vascular calcification and arterial stiffness
• Cognitive impairment
• Progression of kidney disease
• Mortality

The kidney plays a vital role in vitamin D metabolism and regulation. Therefore, impaired renal function, as in the case of CKD, may lead to vitamin D deficiency, as has been observed in patients with CKD (Kim & Kim, 2014). Also, vitamin D deficiency has been associated with a higher risk of cardiovascular disease in patients with CKD and the general population (Nigwekar, et al 2014).

Furthermore, vitamin D deficiency is a common condition in predialysis and dialysis patients with CKD, and levels of vitamin D appear to be linked with kidney function (Nakashima, et al., 2016; Williams, et al., 2010). Recent studies also report that vitamin D intake signifies reduced proteinuria—or the presence of more than normal amounts of protein in the urine—and mortality in CKD patients (Kim & Kim, 2014). Such is beyond the normal role of vitamin D in the maintenance of bone and mineral metabolism.

Prevention is better than cure

Indeed, it is. So what is one simple step to prevent CKD progression then?

Sunlight exposure gives most of us our entire vitamin D requirement. Young adults and children can make all of the vitamin D they need by spending just a few minutes in the sun three times a week. In the case of older people, they have a slightly reduced capacity to synthesize vitamin D, so they need a little more sun. Using sunscreen and wearing protective clothing limits vitamin D production: sunscreen with an SFP factor of 8 curtails production of vitamin D by 95 percent (National Health Service, 2018).

In states and countries located in higher latitudes, there is not enough UVB rays for vitamin D production in the skin for part of the year. Above 40 degrees north, approximately the latitude of Boston or San Francisco, there are four months without enough UVB to make vitamin D. Further north, in Canada, there are five months without much UVB. Vitamin D is stored in the liver for long periods of time (Hossein-nezhad & Holick, 2013). Even for those located in higher latitudes, ten minutes of sun on the arms and face just three times weekly in the spring, summer, and fall will provide enough vitamin D for the whole year. Except for summer months, it is important that this exposure be between 11:00 AM and 2:00 PM so that more UVB will be available. It requires twice the exposure time to the sun at 9:15 AM or 2:15 PM than at noon to provide the same amount of UVB exposure (Harvard Medical School, 2007).

Dark-skinned people living at higher latitudes may need extra vitamin D because their higher level of skin pigmentation may retard the absorption of UVB rays. Also, the weather in higher latitudes reduces daylight hours in winter and may require protective clothing which covers the skin. This is not a problem for those located in tropical areas, where enough vitamin D is provided despite dark skin color. People with very dark skin may only produce 1/6th as much vitamin D as fair-skinned people do in the same amount of time (Hossein-nezhad & Holick, 2013).

Your doctor can test your blood to evaluate your vitamin D levels. Make sure to talk to your medical provider before taking any supplements.