Q: Many of my patients have vitamin D levels drawn. How do I interpret the results?
Vitamin D is a fat-soluble vitamin that the body houses in two forms: D2 and D3, differing in structure and potency (D2 is less potent), but not in function. Starting as an inactive form, vitamin D undergoes two conversions for activation: the liver converts D into calcidiol [25(OH)D], and the kidneys convert it into calcitriol [1,25(OH)2 D]. Serum calcidiol has a longer half-life, so is the preferred way to assess vitamin D status (National Institutes of Health [NIH], 2020). Levels of 21 to 29 ng/mL are considered insufficient, and <20 ng/mL, deficient (Tangpricha et al., 2019).
The vitamin D Recommended Dietary Allowance (RDA) is 600-800 International Units (IU) (Manson, 2020) obtained by three sources: food (naturally or fortified), supplements, and sun exposure (NIH, 2020). Very few foods contain D, with richest sources in fatty fish (salmon, tuna, mackerel), small amounts in beef, liver, cheese, and egg yolks and some in fortified cereals and dairy products (Manson). The Department of Agriculture lists vitamin D-rich foods at http://www.nal.usda.gov/sites/www.nal.usda.gov/files/vitamin_diu.pdf can be used to augment natural D sources and are associated with decreased falls and improved muscle strength in older adults (Tangpricha et al., 2019).
Sunlight supplies most people with a portion of required vitamin D, however, variation occurs with season, cloud/smog covering, sunscreen use, time outdoors, and melanin content (darker skin interferes with D synthesis). Approximately 5 to 30 minutes of sun exposure to the face, limbs and/or back without sunscreen, between 10 a.m. and 3 p.m. at least biweekly is recommended. Sunlight exposure through a window is not effective because ultraviolet-B radiation cannot penetrate glass (NIH, 2020).
Vitamin D promotes numerous health benefits assuming the gut can absorb dietary fat (NIH, 2020). By increasing the efficiency of calcium absorption in the small intestine, vitamin D promotes skeletal health and bone remodeling (Tangpricha et al., 2019). It helps modulate cell growth and neuromuscular function, promotes cardiometabolic health, reduces inflammation, and contributes to immune function by enhancing the body's defenses against viruses (Manson, 2020; NIH). It has been linked to prevention of colon, prostate, and breast cancers (NIH). Vitamin D is being evaluated relative to covid-19 for its immune-modulating and anti-inflammatory effects during the respiratory system's response to cytokine storms and early studies show promise. Vitamin D deficiency has been more prevalent among those with severe covid-19 illness (Manson).
Vitamin D deficiency has been called a silent disease because there are often no overt symptoms. Deficiency occurs among elderly, hospitalized, institutionalized, and healthy young adults (Tangpricha et al., 2019). Causes include decreased dietary intake, impaired absorption, increased excretion, minimal sun exposure, kidney malfunction, and use of drugs that impair vitamin D metabolism or absorption (steroids, cholesterol lowering, antiseizure; NIH, 2020). Older adults are at higher risk for insufficiency due to their skin's inability to synthesize D efficiently, less time outdoors, and/or inadequate intake. Screening is recommended for high-risk groups: Black and Hispanic people, those with osteoporosis, malabsorption syndromes, obesity, and kidney disease (Tangpricha et al.). Deficiency causes skeletal abnormalities such as rickets in children, osteoporosis, osteomalacia with bone weakening, and muscle aches/pains in adults. Inadequate levels cause elevated parathyroid hormones, increase inflammatory biomarkers, and contribute to cancers, diabetes, cardiovascular disease, multiple sclerosis, and rheumatoid arthritis (NIH; Tangpricha et al.).
Adult treatment regimens include D2 or D3 50,000 IU once/week or 6,000 IU/day for 8 weeks. Once levels regulate (>30 ng/mL), suggested maintenance doses are 1,500 to 2,000 IU/day or higher for those at high risk (Tangpricha et al., 2019). Individuals should consult with providers to determine risk level and treatment.
NIH Study Links Cigarette Smoking to Higher Stroke Risk in African Americans
African Americans who smoke are nearly 2.5 times more likely to have a stroke than those who never smoked, while former smokers show a similarly lower risk as never smokers, according to a new study funded by the NIH. The findings from the Jackson Heart Study suggests that even after years of smoking, African Americans - who as a group are twice as likely as whites to have a stroke and die from it - could significantly reduce their risk if they kicked the habit.
Numerous studies have shown the link between smoking and stroke, but few have directly assessed the relationship solely in African Americans. This new study did that and also analyzed traditional risk factors for cardiovascular diseases and inflammation.
The study included 4,410 black men and women without a history of stroke and who were enrolled in the Jackson Heart Study, the largest study of cardiovascular disease in African Americans. Researchers classified the participants, who were 54 on average, into three groups based on their self-reported smoking history: current smokers, past smokers who smoked at least 400 cigarettes in their lifetimes, and never smokers. They further classified current smokers based on smoking intensity. One group included participants who smoked up to 19 cigarettes a day; another included those who smoked 20 or more cigarettes a day. Researchers followed participants from their initial evaluations beginning in 2000 through 2015.
At its start, the study included 781 past smokers, 546 current smokers, and 3,083 never smokers. By 2015, 5.2% of past smokers, 6.6% of those were smoking up to 19 cigarettes a day, and 7.2% of those smokers smoking more than 20 cigarettes a day had experienced a stroke, compared to 3.4% of never smokers.
After accounting for multiple risk factors for stroke, such as high blood pressure, diabetes, high cholesterol, and older age, researchers calculated that current smokers carried a risk for stroke that was more than double the risk for never smokers. And, the risk nearly tripled for those smoking 20 or more cigarettes each day. But past smokers showed an almost identical risk as never smokers.
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