What are some current issues and controversies about vitamin D?

Vitamin D and osteoporosis:

It is estimated that over 25 million adults in the United States have, or are at risk of developing, osteoporosis. Osteoporosis is a disease characterized by fragile bones, and it significantly increases the risk of bone fractures. Osteoporosis is most often associated with inadequate calcium intake. However, a deficiency of vitamin D also contributes to osteoporosis by reducing calcium absorption. While rickets and osteomalacia are extreme examples of vitamin D deficiency, osteopororsis is an example of a long-term effect of vitamin D insufficiency. Adequate storage levels of vitamin D help keep bones strong and may help prevent osteoporosis in older adults, in non-ambulatory individuals (those who have difficulty walking and exercising), in post-menopausal women, and in individuals on chronic steroid therapy. 

Researchers know that normal bone is constantly being remodeled, a process that describes the breakdown and rebuilding of bone. During menopause, the balance between these two systems changes, resulting in more bone being broken down or resorbed than rebuilt. Hormone therapy (HT) with sex hormones such as estrogen and progesterone may delay the onset of osteoporosis. However, some medical groups and professional societies such as the American College of Obstetricians and Gynecologists, The North American Menopause Society, and The American Society for Bone and Mineral Research recommend that postmenopausal women consider using other agents to slow or stop bone-resorption because of the potential adverse health effects of HT.

Vitamin D deficiency, which is often seen in post-menopausal women and older Americans, has been associated with greater incidence of hip fractures. In a review of women with osteoporosis hospitalized for hip fractures, 50 percent were found to have signs of vitamin D deficiency. Daily supplementation with 20 μg (800 IU) of vitamin D may reduce the risk of osteoporotic fractures in elderly populations with low blood levels of vitamin D. The Decalyos II study examined the effect of combined calcium and vitamin D supplementation in a group of elderly women who were able to walk indoors with a cane or walker. The women were studied for two years, and results suggested that such supplementation could reduce the risk of hip fractures in this population. 

All women are encouraged to consult with a physician about their need for vitamin D supplementation as part of an overall plan to prevent and/or treat osteoporosis. 

Vitamin D and cancer:

Laboratory, animal, and epidemiologic evidence suggests that vitamin D may be protective against some cancers. Epidemiologic studies suggest that a higher dietary intake of calcium and vitamin D, and/or sunlight-induced vitamin D synthesis, correlates with lower incidence of cancer. In fact, for over 60 years researchers have observed an inverse association between sun exposure and cancer mortality. The inverse relationship between higher vitamin D levels in blood and lower cancer risk in humans is best documented for colon and colorectal cancers. Vitamin D emerged as a protective factor in a study of over 3,000 adults (96% of whom were men) who underwent a colonoscopy between 1994 and 1997 to look for polyps or lesions in the colon. About 10% of the group was found to have at least one advanced neoplastic (cancerous) lesion in the colon. There was a significantly lower risk of advanced cancerous lesions among those with the highest vitamin D intake.  

Additional well-designed clinical trials need to be conducted to determine whether vitamin D deficiency increases cancer risk, or if an increased intake of vitamin D is protective against some cancers. Until such trials are conducted, it is premature to advise anyone to take vitamin D supplements for cancer prevention. 

Vitamin D and steroids:

Corticosteroid medications such as prednisone are often prescribed to reduce inflammation from a variety of medical problems. These medicines may be essential for medical treatment, but they have potential side effects, including decreased calcium absorption. There is some evidence that steroids may also impair vitamin D metabolism, further contributing to the loss of bone and development of osteoporosis associated with long term use of steroid medications. One study demonstrated that patients who received 0.25 μg of active vitamin D and 1000 mg calcium per day in addition to corticosteroid therapy after a kidney transplant avoided rapid bone loss commonly associated with post-transplant therapy. For these reasons, individuals on chronic steroid therapy should consult with a qualified health care professional about the need to increase vitamin D intake through diet and/or dietary supplements.

Vitamin D and Alzheimer's disease:

Alzheimer's disease is associated with an increased risk of hip fractures. This may be because many Alzheimer's patients are homebound, frequently sunlight deprived, and older. With aging, less vitamin D is converted to its active form. One study of women with Alzheimer's disease found that decreased bone mineral density was associated with a low intake of vitamin D and inadequate sunlight exposure. Physicians should evaluate the need for vitamin D supplementation as part of an overall treatment plan for adults with Alzheimer's disease.

Vitamin D and caffeine:

High caffeine intake may accelerate bone loss. Caffeine may inhibit vitamin D receptors, thus limiting absorption of vitamin D and decreasing bone mineral density. A study found that elderly postmenopausal women who consumed more than 300 milligrams per day of caffeine (which is equivalent to approximately 18 oz of caffeinated coffee) lost more bone in the spine than women who consumed less than 300 milligrams per day. However, there is also evidence that increasing calcium intake (by, for example, adding milk to coffee) can counteract any potential negative effect that caffeine may have on bone loss. More evidence is needed before health professionals can confidently advise adults to decrease caffeine intake as a means of preventing osteoporosis. 

Effects on Calf Performance (Milk Replacer VS Whole Milk)

Introduction

The use of pasteurized waste (i.e., nonsalable) milk as a liquid feed for calves has increased in recent years (NAHMS 2002; NAHMS 2007) due to greater availability of on-farm pasteurizers. Properly pasteurized waste milk can be a high-quality source of nutrients for young calves, and is oftentimes thought of as supporting superior calf health and performance compared with conventional milk replacer programs. This view is accurate when considered in the context of nutrient concentration; pasteurized waste milk often contains much greater concentrations of protein and fat (Jorgensen et al., 2006) and will likely result in greater crude protein and fat intake compared with a conventional milk replacer program. The primary areas of concern with pasteurized waste milk are bacterial contamination, variation in nutrient intake, and the low concentrations of vitamins and minerals compared with milk replacer.

Godden et al. (2005) reported that feeding pasteurized waste milk (1 gallon/calf per day) increased average daily gain (ADG) and decreased morbidity and mortality compared with calves fed a 20-20 milk replacer (1.0 lb powder/calf per day). Dry matter (DM), protein, and fat concentrations in pasteurized waste milk were not reported, but distinct differences in nutrient intake between groups would be expected considering that the pasteurized waste milk contained various amounts of transition milk (Godden et al., 2005). The differences in calf performance are not surprising under the conditions of the study.

Recent research has compared raw (Hill et al., 2008) and pasteurized (Hill et al., 2007) salable whole milk (not waste milk) with conventional milk replacers and reported the effect of liquid feed source on calf performance. These studies are novel because daily dry matter intake (DMI) was equalized between the whole milk and milk replacer treatments, thus the primary difference among treatments was the protein and fat concentration in the whole milk. This article summarizes these studies with emphasis on the calf performance data.

Study 1: Raw Milk versus Conventional Milk Replacer (Hill et al., 2008)

The trial used Holstein bull calves purchased from multiple dairy farms. Calves were fed their liquid feed source twice daily from d 0 to 39, and once daily from d 40 to 42. All calves were offered ad libitum access to a 20.4% CP (DM basis) pelleted calf starter and fresh water from d 0 to 56. The trial was conducted from February to April where the average temperature was 37.4°F (range of 3.2° to 68°F).

Three treatments (16 calves per treatment) differing in source of liquid feed were used in this study: 1) 1.0 lb/day (as-fed) of a 20-20 milk replacer powder in 1 gallon of total solution (MR), 2) 50% of DM from MR, 50% of DM from raw salable milk (MR+milk), and 3) all DM from raw salable milk (Milk). The DM content of raw salable milk was monitored regularly throughout the trial to maintain equivalent DMI among treatments, which meant that the total volume of liquid feed offered to the calves differed among treatment due to fluctuations in raw milk DM. The MR used in this study contained supplemental L-Lysine and DL-Methionine, and the fat source was a combination of animal and vegetable fat.

Raw salable milk averaged 13.6% DM (range of 10.5-15.0%), 25.3% CP (range of 24.5-25.9%), and 27.6% fat (range of 25.9-28.5%). Nutrient intake and calf performance measurements are presented in Table 1. Calves fed 100% MR consumed less protein, fat, and metabolizable energy (ME) from their liquid feed than did calves fed MR+milk and 100% milk. However, total protein and ME intake was similar among groups due to greater starter intake by calves fed 100% milk replacer, whereas total fat intake remained higher for calves fed 50% or 100% raw salable milk. According to these data, calf body weight on d 42 of the trial was 132, 126, and 125 lbs for MR, MR+milk, and Milk treatments, respectively.

 

Study 2: Pasteurized Milk versus Two Conventional Milk Replacers (Hill et al., 2007) 

This trial used Holstein bull calves purchased from multiple dairies. Liquid feeds were fed from d 0 to 42. All calves were offered ad libitum access to an 18% CP (as-fed basis) pelleted calf starter from d 3 to 56 and had access to fresh water at all times. This trial was conducted from September through November.

Treatments were arranged as a 3 × 2 factorial with 3 sources of liquid feed DM fed at 2 rates of DMI (6 treatments, 8 calves/treatment). The 3 liquid feed sources were: 1) 22-20 all-milk protein MR with no supplemental amino acids and lard as the sole fat source (CON22), 2) 20-20 all-milk protein MR with supplemental amino acids (L-Lysine and DL-Methionine) and specific fatty acids (provided by sodium butyrate, coconut oil, canola oil, and lard) (MOD20), and 3) pasteurized whole milk (MILK). The low feeding rate of each liquid feeding source was intended to match the DM provided by 1.0 lb of milk replacer powder (as-fed basis), whereas the high feeding rate was intended to match the DM provided by 1 gallon of pasteurized whole milk. The nutrient composition (as-fed basis) of pasteurized milk was 14% DM, 3.2% CP, and 3.6% fat, which is equal to 22.9% CP and 25.7% fat on a DM basis. Nutrient intake and calf performance measurements for the main effect of liquid feed source are presented in Table 2.

Calves that were fed the MOD20 milk replacer had the greatest ADG compared with calves fed CON22 or MILK. Calf body weight on d 42 was 123, 132, and 125 lbs for the CON22, MOD20, and MILK treatments, respectively. In this study, starter intake did not differ despite differences in total fat intake.

Discussion

The research summarized here demonstrated that a well-formulated milk replacer can support equivalent or greater calf performance despite differences in dietary CP and fat concentrations compared with whole milk. The increased performance of calves fed certain milk replacers appears to be due to supplementing specific amino acids and/or altering the fatty acid profile of the milk replacer (Hill et al., 2007, 2008).

Regardless of the mechanism responsible, these papers further support the notion that all milk replacers are not created equal despite what is listed on the tag, and that properly-formulated conventional milk replacers can support equal or improved calf performance than whole milk when equalized for total DMI.

Source :  
www.milkproductsinc.com
www.certifeed.com