VITAMIN D

Tldr; Dairy appears to be the best food source for vitamin D3. Cod liver oil effectiveness varies, depending on the processor and the method of analysis. While the previous Recommended Dietary Allowance (RDA) for Vitamin D was adequate to prevent rickets in children, it is now considered insufficient for adults. Research suggests that higher levels of Vitamin D intake are necessary to maintain optimal health in adults.

Various factors such as latitude, skin tone, and environmental conditions can affect the rate of Vitamin D synthesis from sunlight. Of these factors, latitude and skin tone appear to be the most influential.

Those living closer to the equator have a greater ability to produce Vitamin D through sunlight exposure, while individuals with darker skin tones are at a higher risk of Vitamin D deficiency. In fact, it has been observed that areas located above latitude 42.2°N, such as Boston, fail to produce any UVB-induced previtamin D from November to February, a period of four months. This deficiency in Vitamin D synthesis is further prolonged to six months above latitude 55°N, as observed in Edmonton. However, regions located within the range of 18-32°N still produce Vitamin D during the winter.

Sunscreen is able to significantly diminish synthesis of vitamin D, and chronic usage may be associated with vitamin D deficiency, if no oral supplementation exists.

Vitamin D3, also called cholecalciferol, is the common supplement for vitamin D. It is better absorbed compared to other forms of vitamin D.

The activation of Vitamin D3 into its hormone form involves either two stages (if starting from a dietary supplement containing Vitamin D3) or three stages (if starting from skin stores). The skin initiates the first (non-supplemental) conversion, while the liver and kidneys mediate the later two metabolic steps.

Both vitamin D2 and D3 can be used as supplements to increase circulating levels of the active hormone. While some studies suggest that D3 is more effective than D2, others argue that the potency difference can be normalized by standardizing to an IU value.

There is conflicting evidence regarding the effectiveness of vitamin D2 and D3 when compared on an IU basis. Some studies have found them to be bioequivalent, while others suggest a superiority of vitamin D3. However, there are no studies suggesting that D2 is more effective than D3. As a result, it is recommended to choose D3 supplementation.

There are differences in the synthesis and stability of D2 and D3, which are two forms of vitamin D used for supplementation. D3 is synthesized differently from D2 and is more stable than D2 in powder form.

Recommended levels of vitamin D are roughly 75nmol/L (30ng/mL) for some conditions.

Deficiency rates in the population appear to have increased over the past two decades but they may have stabilized in recent years.

Although latitude is a significant factor, it is important to note that vitamin D deficiency (defined by serum levels of 25nmol/L or below) and insufficiency (50nmol/L), are prevalent globally.

In general, a dose of 2,000 IU is sufficient to fulfill the vitamin D needs of most individuals. Doses ranging from 2,000-10,000 IU may not provide any additional benefits, but are not considered toxic either.

Regarding dosing, lower oral doses appear to be more effective in increasing serum vitamin D levels than higher doses, which may have reduced absorption. This variability between individuals suggests that different doses may be needed to achieve the desired level of serum vitamin D. At lower ranges of oral dosing, vitamin D seems to have a linear effect on serum levels, with each 100IU increasing serum by approximately 1-2nmol/L. For instance, 1,000IU is implicated in the range of 10-25nmol/L and 2,000IU in the range of 20-50nmol/L.

Vitamin D is best absorbed with a meal, preferrably one with a little fat in it.

Toxicity has been noted at very high _daily_ doses of vitamin D, which are about 10-fold higher than the aforementioned 2,000IU daily dose.

Vitamin D3 appears to be a more reliable form of supplemental vitamin D, relative to D2, for increasing serum levels to an adequate range.

Several observational studies have reported a negative association between serum vitamin D levels and all-cause mortality.

Clinical trials investigating the impact of vitamin D supplementation on mortality rates have suggested a small reduction in all-cause mortality, particularly in older adults.

Vitamin D3 supplementation appears to be the most efficient form of supplementation for reducing mortality.

It is possible that vitamin D might serve as a biomarker for another factor that is related to longevity. However, there is currently no evidence to suggest that vitamin D supplementation can increase lifespan directly. Rather, it appears that supplementation may indirectly reduce the risk of premature death.

In vitro and animal data suggest that vitamin D can modulate a subset of calcium channels on neurons and regulate cell death through excitotoxicity.

There is evidence of an inverse relationship between vitamin D levels in the blood and symptoms of depression in certain groups.

Multiple Sclerosis (MS) prevalence is correlated with latitude and sun exposure, both of which are in turn correlated with vitamin D levels.

There does appear to be some, albeit weaker, correlation between Alzheimer’s disease and vitamin D.

Low serum vitamin D is correlated with increased risk of Parkinson’s Disease (PD) and further associated with the severity of the disease state.

Observational studies have indicated that low vitamin D levels are linked to an increased risk of cardiovascular disease.

Vitamin D levels have been inversely correlated with insulin resistance and insulin sensitivity in non-diabetic adults.

Daily supplementation of 4000IU appears to lead to improved performance in athletes along with muscle recovery after damage induced by eccentric exercise. A correlation between low Vitamin D levels, illness and athletic injuries appears to exist, especially in regards to stress fractures.

Vitamin D acting upon its receptor does promote mineralization of bone tissue and is correlated with less risk for fractures in the youth. Specifically, vitamin D supplementation appears to further protect individuals from stress fractures.

Vitamin D in serum appears to be positively correlated with overall androgen status, with sufficient levels of vitamin D acting to normalize testosterone. There is currently no evidence to suggest supraphysiological levels of vitamin D further enhances testosterone.

Vitamin D in serum appears to be inversely related to breast cancer risk (higher serum levels being associated with lower risk).

Furthermore, Vitamin D deficiency appears to be more prevalent in persons with diagnosed breast cancer and is similarly correlated with severity of breast cancer. 400-800IU daily appears to be inadequate to decrease the risk of breast cancer, whereas women supplementing with 2000IU of Vitamin D daily, may see up to a 50% reduction in the incidence of breast cancer.

Evidence suggests that even though 1000IU per day is somewhat effective in improving Vitamin D status, a weekly administration of 50,000IU is more effective.

Vitamin D appears to be inversely correlated with risk of colon and colorectal cancers, as well as with  Prostate and Ovarian cancer.

For colorectal cancer outcomes, a reduction was observed with 2000IU of supplemental Vitamin D. Additionally, doses as low as 600IU/d lower the risk of pancreatic cancer.

Higher serum Vitamin D appears to be associated with improved lung function as assessed by forced exhalation.

Low levels of Vitamin D are associated with increased corticosteroid use in asthmatic children while supplementation of 1200IU daily is associated with decreased asthmatic attacks in children previously diagnosed with Asthma.

Children taking 1200IU of Vitamin D daily are 40% less likely to get the flu during the winter and supplementing with Vitamin D will help prevent the flu on adults.

Vitamin D also appears to be correlated with sleep quality.

Mechanistically, vitamin D appears to act on the sperm itself (mature spermatid) and improve its motility while enhancing cell survival. 25-50ng/mL (62.4-124.8nmol/L) appears to be an adequate range to preserve optimal seminal properties in otherwise healthy men.

Research suggests that pregnant women have lower serum vitamin D levels compared to non-pregnant women, and this deficiency can have adverse effects on both the mother and the child.

The deficiency is particularly critical during the first trimester, and therefore, supplementing vitamin D only after pregnancy notification may not be the best approach as it may miss the time-sensitive period.

A slightly higher intake of vitamin D may be required to reach sufficiency in pregnant women, relative to nonpregnant women and men, with intakes of up to 4,000IU being advised.

Vitamin D is potentially synergistic with Vitamin K supplementation as the two share many mechanisms of action in the cardiovascular and bone metabolism systems and people with mean serum levels of 86.5 nmol/L had 65% better absorption of calcium than people with mean serum levels of 50 nmol/L.