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Factors Increasing Vitamin D Absorption
Introduction to Vitamin D Absorption
Vitamin D is essential for maintaining bone health and supporting the immune system. However, the absorption of vitamin D can vary significantly based on several factors, including diet composition and the presence of certain nutrients. This article synthesizes research findings on the factors that enhance vitamin D absorption.
Dietary Fat and Vitamin D Absorption
Fat-Containing Meals
Research indicates that the presence of dietary fat significantly enhances the absorption of vitamin D. A study involving healthy older adults found that consuming a vitamin D supplement with a fat-containing meal increased plasma vitamin D-3 levels by 32% compared to a fat-free meal 1. This suggests that dietary fat plays a crucial role in facilitating the absorption of vitamin D.
Types of Fat: MUFA vs. PUFA
While the presence of fat is important, the type of fat—whether monounsaturated (MUFA) or polyunsaturated (PUFA)—does not significantly affect vitamin D absorption. The same study found no significant difference in vitamin D absorption between meals with high MUFA and high PUFA ratios 1.
Mechanisms of Vitamin D Absorption
Passive Diffusion and Membrane Carriers
Vitamin D absorption is not solely a passive diffusion process. It also involves membrane carriers, particularly cholesterol transporters. This dual mechanism means that factors affecting cholesterol absorption can also influence vitamin D absorption 2.
Role of Cholesterol Transporters
Cholesterol transporters play a significant role in the absorption of vitamin D. This is supported by findings that modifications in cholesterol absorption can alter vitamin D absorption, highlighting the interconnected nature of these processes 2.
Vitamin D Supplementation and Calcium Absorption
Dose-Response Relationship
Vitamin D supplementation increases calcium absorption, but there is no clear threshold beyond which higher doses of vitamin D no longer enhance calcium absorption. Studies have shown a linear increase in calcium absorption with increasing doses of vitamin D, without evidence of a plateau effect 34.
Impact of Weight Loss
Weight loss can decrease calcium absorption, but vitamin D supplementation can mitigate this effect. A study on postmenopausal women found that vitamin D supplementation increased true fractional calcium absorption (TFCA) even during weight loss, suggesting that adequate vitamin D intake is crucial for maintaining calcium balance during weight reduction 5.
Vitamin D in Different Populations
Children and Vitamin D Absorption
In children, vitamin D supplementation increases serum 25-hydroxyvitamin D levels but does not significantly enhance calcium absorption. This was observed in studies involving both healthy prepubertal children and those with nutritional rickets, indicating that other factors may influence calcium absorption in younger populations 679.
Young Women and Vitamin D Absorption
In young women with vitamin D insufficiency, supplementation did not increase calcium absorption, even at higher doses. This suggests that in populations with adequate dietary calcium and phosphorus, vitamin D may not significantly impact calcium absorption 8.
Conclusion
The absorption of vitamin D is significantly enhanced by the presence of dietary fat, although the type of fat does not appear to matter. The process involves both passive diffusion and membrane carriers, particularly cholesterol transporters. While vitamin D supplementation can increase calcium absorption, this effect varies across different populations and is influenced by factors such as weight loss and baseline vitamin D levels. Understanding these factors can help optimize vitamin D supplementation strategies for different individuals.
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Most relevant research papers on this topic
Dietary fat increases vitamin D-3 absorption.
Vitamin D-3 supplementation is more effectively absorbed when taken with a meal containing fat, but the ratio of monounsaturated to polyunsaturated fatty acids in the fat does not influence its absorption.
RCT
Highly CitedIntestinal absorption of vitamin D: a systematic review
Vitamin D absorption involves passive diffusion and membrane carriers, with some data suggesting that fat consumption with vitamin D improves absorption.
Systematic ReviewHighly CitedVitamin D supplementation increases calcium absorption without a threshold effect.
Vitamin D supplementation increases calcium absorption without a threshold effect, making it unsuitable for determining vitamin D nutritional recommendations.
RCT
Very Rigorous JournalHighly CitedThe effect of vitamin D on calcium absorption in older women.
High doses of vitamin D3 do not significantly increase calcium absorption in postmenopausal women, and the same amount could be obtained from half a glass of milk or 100 mg elemental calcium.
RCTVitamin D supplementation and calcium absorption during caloric restriction: a randomized double-blind trial.
Vitamin D supplementation increases calcium absorption and maintains calcium balance during weight loss, suggesting it is sufficient for maintaining calcium balance when calcium intake is 1.2 g/d.
RCTVery Rigorous JournalSupplementation with 1000 IU vitamin D/d leads to parathyroid hormone suppression, but not increased fractional calcium absorption, in 4-8-y-old children: a double-blind randomized controlled trial.
Vitamin D3 supplementation at 1000 IU/d increases 25(OH)D and decreases parathyroid hormone in children with average vitamin D intake below dietary recommendations, but does not significantly affect calcium absorption.
RCTVery Rigorous JournalThe effect of vitamin D2 and vitamin D3 on intestinal calcium absorption in Nigerian children with rickets.
Vitamin D2 and vitamin D3 both increased 25-hydroxyvitamin D levels, but did not significantly affect fractional calcium absorption in Nigerian children with rickets.
RCT
Rigorous JournalHighly CitedVitamin D Does Not Increase Calcium Absorption in Young Women: A Randomized Clinical Trial
Vitamin D does not increase calcium absorption in young women with vitamin D insufficiency, suggesting no need to recommend it for this purpose in normal subjects.
RCTRigorous JournalA Randomized Trial of Vitamin D3 Supplementation in Children: Dose-Response Effects on Vitamin D Metabolites and Calcium Absorption
Vitamin D3 supplementation increases serum 25(OH)D levels but does not increase calcium absorption in healthy children at different latitudes.
RCT
Large Human TrialRigorous JournalHighly CitedStimulation of intestinal calcium absorption by orally administrated vitamin D3 compounds: a prospective open-label randomized trial in osteoporosis
Oral vitamin D3 analogues (ALF and ELD) stimulate intestinal calcium absorption in post-menopausal osteoporosis patients, suggesting they may directly stimulate intestinal vitamin D receptors.
RCTRigorous Journal